227 lines
8.6 KiB
Plaintext
227 lines
8.6 KiB
Plaintext
---
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title: "How I convert PDFs to EPUB semi-automatically"
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slug: how-i-convert-pdfs-to-epub
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description: "A step by step guide to clean EPUBs from PDFs using Calibre, Emacs and time."
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date: 2021-03-15T04:12:00+01:00
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type: posts
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draft: false
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tags:
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- EPUB
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- E-books
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- Emacs
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toc: true
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---
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:source-highlighter: pygments
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:experimental: true
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:toc:
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:toclevels: 2
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:url-calibre: https://calibre-ebook.com/
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:url-calibre-convert: https://manual.calibre-ebook.com/conversion.html#pdfconversion
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:url-emacs: https://www.gnu.org/software/emacs/
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:url-emacs-key-notation: https://www.emacswiki.org/emacs/EmacsKeyNotation
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:wp-pdf: https://en.wikipedia.org/wiki/PDF
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:wp-epub: https://en.wikipedia.org/wiki/EPUB
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:wp-xhtml: https://en.wikipedia.org/wiki/XHTML
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:wp-css: https://en.wikipedia.org/wiki/CSS
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Sometimes e-books come only in link:{wp-pdf}[PDF] format. Almost always PDFs are
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a pain to read on e-book readers. You can use link:{url-calibre}[Calibre] to
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automatically convert it, but link:{url-calibre-convert}[the results are
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okay-ish at best]. If the PDF has footnotes, forget it. Unfortunately, the type
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of books that most often come only as PDFs are science books and these usually
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have a lot of footnotes.
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One option is to use Calibre to convert and then fix the result, but I have
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found that I get better results in less time when I create a new
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link:{wp-epub}[EPUB], copy the PDF's content into link:{url-emacs}[Emacs], clean
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it up there and then copy it over to Calibre. This process is what I want to
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share with you here. You will need Calibre, Emacs or another editor with
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keyboard macros and some knowledge of link:{wp-xhtml}[XHTML] and
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link:{wp-css}[CSS] to follow this guide. It will take long and is boring, but
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the result is a clean and enjoyable book.
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[NOTE]
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I will use the link:{url-emacs-key-notation}[Emacs key notation] throughout this
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guide.
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== Create a new book in Calibre
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Click on menu:Add books[Add empty book]. Then fill in the metadata and select
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“EPUB” as format. You can add more metadata and a cover image by right-clicking
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the book and then selecting menu:Edit metadata[]. Open Calibre's editor by right
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clicking on the book and selecting menu:Edit book[]. You start with a single XHTML
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file, `start.xhtml`. I always use that for the title page, the copyright notice
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and so on. You can force a page break to separate the title and the copyright
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notice with CSS: Add `style="page-break-after: always;"` to the last element of
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the virtual “page” or use a CSS class. To add a CSS file click menu:File[New
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file] and enter a filename ending with `.css`. Add the CSS file to the document
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by right clicking on `start.xhtml` in the file browser and selecting
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menu:Link stylesheets…[].
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[NOTE]
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The built-in preview does not show page breaks.
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Your files should look similar to this:
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.`start.xhtml`
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[source,html]
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--------------------------------------------------------------------------------
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<?xml version='1.0' encoding='utf-8'?>
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
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<head>
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<title>Meine zwei Jahre in Russland</title>
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<link rel="stylesheet" type="text/css" href="style.css"/>
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</head>
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<body>
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<div class="pagebreak center" id="title">
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<p>Emma Goldman</p>
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<h1>Meine zwei Jahre in Russland</h1>
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</div>
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<p>1. Auflage<br/>
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München, Januar 2020</p>
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<p id="copyright">Anti-Copyright (siehe S. 362)</p>
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<p>Die englische Originalausgabe erschien 1921 und 1925 in den
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USA aufgrund eines Versehens in zwei Teilen unter den Titeln
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<em>My Disillusionment in Russia</em> und <em>My Further Disillusionment in
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Russia.</em></p>
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</body>
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</html>
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--------------------------------------------------------------------------------
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.`style.css`
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[source,css]
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--------------------------------------------------------------------------------
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.pagebreak {
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page-break-after: always;
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}
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.center {
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text-align: center;
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}
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--------------------------------------------------------------------------------
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I added the IDs “title” and “copyright” to add semantic links to them later.
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=== Some styling advice
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Please refrain from using CSS too much. Most people have configured their e-book
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readers the way they like, with the right font, font-size, margins and so on. If
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you override their settings, they will be annoyed. I usually only style the
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title page and headlines.
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Do not use `<i>` or `<b>` tags to emphasize, do not use `font-style: italic` or
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`font-style: bold`. Use `<em>` for emphasis and `<strong>` for
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importance so screen readers will be able to pronounce the text differently.
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== Add text to the book
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Add a new `.xhtml` file in Calibre and write in the heading of the first
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chapter. Then switch to Emacs and copy the first paragraph from the PDF into a
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`text-mode` buffer. The emphasis will not be copied over, so you'll have to
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re-add it. We ignore (but keep) the footnote numbers for now. Repeat with the
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rest of the paragraphs of the chapter, leaving 2 blank lines between each
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paragraph. The paragraphs will be broken and likely be full of hyphens at the
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end of the lines.
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.elisp function to add HTML tags easily
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[source,elisp]
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--------------------------------------------------------------------------------
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(defun my/html-surround-with-tag (beg end)
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"Surround region with HTML tag."
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(interactive "*r")
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(if (region-active-p)
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(let ((tag (completing-read "Tag: "
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'("blockquote" "em" "strong"))))
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(insert (concat "<" tag ">"
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(delete-and-extract-region beg end)
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"</" tag ">")))
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(message "No active region")))
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--------------------------------------------------------------------------------
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Make sure that `auto-fill-mode` is disabled. Position the cursor at the start of
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the buffer and press kbd:[<f3>] to start recording a macro. Press kbd:[<end>]
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kbd:[<deletechar>] kbd:[SPC] (space bar) and then kbd:[<f4>] to stop
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recording. If there is a hyphen at the end of the current line, press
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kbd:[<backspace>] 2 times. Press kbd:[<f4>] to call the macro and repeat until
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you are at the end of the paragraph. Move the cursor to the first line of the
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next paragraph and repeat…
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Now you should have a text file with 1 paragraph per line. We need to wrap all
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lines in `<p>` tags, except block quotes and sub-headlines. Either use another
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macro (`<p>` kbd:[<end>] `</p>` kbd:[<down>] kbd:[<down>] kbd:[<home>]) or this
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elisp function:
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[source,elisp]
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--------------------------------------------------------------------------------
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(defun my/html-paragraphify-buffer ()
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"Wrap every line not beginning with < or a newline in <p> tags."
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(interactive)
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(goto-char (point-min))
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(while (re-search-forward "^\\([^<
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].+\\)$" nil t)
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(replace-match "<p>\\1</p>")))
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--------------------------------------------------------------------------------
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Once you are done, copy the result into Calibre.
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== Add footnotes
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Use the method from above to copy the footnotes into the now empty Emacs buffer
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and clean them up until you have 1 paragraph per line. Footnotes need to be
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hyperlink-able, so we can't just wrap them in plain `<p>` tags, they need IDs. I
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like to use `<span>1</span><p id="fn1">[…]</p>` if there is only one
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footnote-section or `<span>1</span><p id="fn1_1">[…]</p>` for
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chapter-footnotes. We are going to use a macro with a counter to generate
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consecutively numbered IDs. First, set the counter to 1 with kbd:[C-x]
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kbd:[C-k] kbd:[C-c] `1`. Then, record this macro:
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`<span>` kbd:[C-x] kbd:[C-k] kbd:[<tab>] kbd:[C-u] `-1` kbd:[C-x] kbd:[C-k]
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kbd:[C-a] `</span><p id="fn` kbd:[C-x] kbd:[C-k] kbd:[<tab>] `">` kbd:[<end>]
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`</p>` kbd:[<down>] kbd:[<down>] kbd:[<home>]
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[NOTE]
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kbd:[C-u] `-1` kbd:[C-x] kbd:[C-k] kbd:[C-a] “adds” -1 to the counter, so that
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we can use the same number again.
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Call the macro until every footnote is wrapped and copy them to Calibre.
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=== Add references to footnotes
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The footnotes are probably superscript numbers in the PDF but normal numbers in
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the EPUB right now. I found that the footnote-numbers are usually preceded by a
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space and followed by a space or `<`. I use the find & replace function in
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Calibre in Regex-mode to convert them to hyperlinks.
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Find: `` ([0-9]{1,3})([ <])`` (note the leading space) +
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Replace: `<sup><a href="#fn\1">\1</a></sup>\2`
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Press kbd:[<f3>] to search through the text and kbd:[C-r] to replace.
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== Finishing touches
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Click menu:Tools[Table of Contents > Edit table of Contents], remove the
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existing entry and click btn:[Generate ToC from major headings] or btn:[Generate
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ToC from all headings].
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Click menu:Tools[Set semantics] and set the location of the title page,
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copyright page, beginning of text and so on.
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Select menu:Tools[Check book] and fix the errors.
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You're done! Enjoy your cleanly formatted book. 😊
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// LocalWords: Calibre
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