Add PDF → EPUB article.
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content/posts/how-i-convert-pdfs-to-epub.adoc
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content/posts/how-i-convert-pdfs-to-epub.adoc
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---
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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 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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---
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:source-highlighter: pygments
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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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: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'd like 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 recipe. It will take long and is boring, but
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the result is a clean and enjoyable book.
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== Create a new book in Calibre
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Click on “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 “Edit metadata”. Open Calibre's editor by right
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clicking on the book and selecting “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 “File” → “New
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file” and enter a filename ending with `.css`. Add the CSS file by right
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clicking on `start.xhtml` in the file browser and selecting “Link
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stylesheets…”. Note that the in-built 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 `<f3>` to start recording a macro. Press `<end>`
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`<deletechar>` `SPC` (space bar) and then `<f4>` to stop recording. If there is
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a hyphen at the end of the current line, press `<backspace>` 2 times. Press
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`<f4>` to call the macro and repeat until you are at the end of the
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paragraph. Move the cursor to the first line of the 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>” `<end>` “</p>” `<down>` `<down>` `<home>`) or this 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 `C-x C-k
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C-c` “1”. Then, record this macro:
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“<span>” `C-x C-k` `<tab>` `C-u` “-1” `C-x C-k C-a` “</span><p id="fn” `C-x C-k`
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`<tab>` “">” `<end>` “</p>” `<down>` `<down>` `<home>`
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`C-u` “-1” `C-x C-k C-a` “adds” -1 to the counter, so that we can use the same
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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 `<f3>` to search through the text and `C-r` to replace.
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== Finishing touches
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Click “Tools” → “Table of Contents” → “Edit table of Contents”, remove the
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existing entry and click “Generate ToC from major headings” or “Generate ToC
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from all headings”.
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Click “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 “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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