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I was wondering how to view and edit the code of a pdf file?

  1. By viewing, I don't want to see the binary format, so I think hexdump may not be what I want. I tried gedit, but no encoding method can be used to decode the pdf content.
  2. By editing, I would like to search for /Fit and change them to /XYZ by for example sed. But my command sed s/\/Fit/\/XYZ/ < 1.pdf > 2.pdf seem not change the appearance of my pdf as I expected, although it doesn't report any error. I was wondering if sed can actually work on pdf files as if they were plain text?

The context of my questions can be found from this question. My OS is Ubuntu 10.10.

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2 Answers

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You can use sed with binary files (at least GNU sed; some implementations may have trouble with files containing null characters or not ending with a newline character). But the command you used only replaces the first occurrence of /Fit on each line, and lines are pretty much meaningless in a PDF file. You need to replace all occurrences:

 sed s/\/Fit/\/XYZ/g

It would be more robust only replace /Fit if it's not followed by a word constituent (e.g. not replacing /Fitness; I don't know if your file contains occurrences of /Fit that would cause trouble). Here's one way:

perl -pe 's!/Fit\b!/XYZ!g'
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Thanks! It now works! (1) I was wondering how sed search characters in binary content? Does sed firstly encode the query characters before search? (2) In the last command, what does !, \b and g mean? Can it be done without perl just with sed? – Tim Jul 22 '11 at 14:00
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@Tim (1) Sed loads the data into memory, operates on it and prints it out. Why would it need to encode anything? (2) g means to replace all occurrences on each line, in both sed and perl. ! is the separator; you can choose (almost) any character as the separator for the s command (this goes both in sed and perl). \b means a word boundary; it exists in perl but not in sed. – Gilles Jul 22 '11 at 14:05
About (1), because the characters that you give to sed in the command are human readable. If the content to search in is completely binary, how can sed find the query word there? – Tim Jul 22 '11 at 14:08
@Tim Text is binary data that happens to be human readable. – Gilles Jul 22 '11 at 14:20
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@Tim Yes, you can pass binary data in the query. You'll have to insert the characters literally in your sed or shell source code. – Gilles Jul 22 '11 at 14:30
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sed is line-oriented, that makes it not well suited for binary files, which are structured as blocks not lines.
Try using bbe (bbe-.sourceforge.net) instead.

Alternatively, both Emacs (GNU and XEmacs) and vim open PDF files seamlessly. It's not very pretty printed of course, as it is mixed text and binary, but it's sufficient for your editing purposes.
There is a Pdftk plugin for vim that makes everything easier, download here (zip file).
As you probably know, both above editors have powerful search-and-replace capabilities.

Also, converting the PDF to QDF mode before makes editing PDF files really easy.

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You may also try to edit with sed using the -b switch. if it works I will add this to my answer. – Philomath Jul 22 '11 at 13:03
@Tim: what do you mean by "does not show anything", just empty? any error message? Also, can you try with XEmacs ? (all three of them worked for me). – Philomath Jul 22 '11 at 13:17
Never mind about -b, it's cygwin specific. – Philomath Jul 22 '11 at 13:18
Emacs says "File 1.pdf is large (9MB), really open? (y or n)". I chose "y", and then nothing is there. – Tim Jul 22 '11 at 13:30
Most probably a Emacs problem, do you have XEmacs? (I just opened a 31 MB PDF without any problems). – Philomath Jul 22 '11 at 13:36
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