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Posted on 2023-11-27 at 10:19:00 by Phil
Last update on 2023-11-29 at 11:19:00 by Phil
Something I’ve requested on the Adobe Community Forums (Adobe Acrobat Reader support) is a good PDF (Portable Document Format) debugger or analyzer. This goes beyond simply dumping a PDF file in a readable format — it would look through the file and examine it for (at least) the following items:
That ought to take care of a lot of common errors. More edge and corner cases could be added over time.
Should anyone implement such a utility, whether free/open source or for pay, please let me know so I can put a pointer to it in here!
Further discussion (appendable) in https://github.com/PhilterPaper/Perl-PDF-Builder/issues/199 .
Posted on 2023-11-27 at 11:22:00 by Phil
Even before implementing a debugger/analyzer, a useful set of tools would be utilities to “dump” and “undump” a PDF file to and from a text (flat) file. This would permit a user to easily view the innards of a PDF, modify it with a normal text editor, and write it back out into a usable PDF file.
The text file would not necessarily have any analysis or debugging done; just a clean dump of the contents, without any specific labeling or indication of what something is. Such extra material might be added by the user, and removed during output.
Note that even if you “round trip” a PDF file, there’s no guarantee that the resulting PDF will be byte-for-byte identical to the original PDF! It should be functionally identical, but may be slightly different internally. All stream lengths and object offsets will be recalculated and may change.
Should anyone implement such a utility, whether free/open source or for pay, please let me know so I can put a pointer to it in here!
Posted on 2023-12-01 at 14:31:00 by Phil
Another item of interest in debugging a PDF, is finding out why certain images display correctly on some readers, but not on others. The error may be a blank screen, or a message that there is insufficient data.
There are many image formats, each with numerous variants, and different compression methods. It may not be possible for the image-checking section of a debugger to handle everything, but perhaps we can make a start. At least, we can output a warning that something was found that is known to work on some Readers, but may not on others.
Somewhere in the header for an image object should be information on what compression method is being used. That could be checked for compatibility with a range of Readers. The data stream length can also be checked, but if it’s the expanded (decoded) data, the debugger would have to be able to uncompress the data, after which it could confirm that there is a correct amount of data. This should be possible, but is a lot of work.
Different image formats have different ways of arranging data, which not all Readers may support. For example, TIFF’s CCITT Group 4 fax has some data arrangements that apparently few Readers support. If this data is hidden within the data stream itself, and not in the object header, it may not be possible for a debugger to spot the possible problem (informing the user that a certain format is in use, which may cause problems).
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