One of our clients has two of his PDF files corrupted. Trying to open the file from Acrobat Reader, and all you get is an error message prompting you "There was an error opening this document. The file is damaged and could not be repaired." Since those PDF files were previously saved into the document management system that I designed, somehow it became my responsibility to return sanity to his files.
Anyway, the customers are always right.
So I began my request repairing these corrupted PDF files. Being an Open Source die-hard, obviously I would give FOSS solutions a try first. Both Google and Yahoo search revealed nothing. All the existing command-line ghostscript or pdf2blah bark at those files, telling me that cross-reference table cannot be rebuild, and nothing can be extracted out.
Then through a forum I was referred to pdftk -- the PDF toolkit. The main functionality is for merging and splitting multiple PDF files, but it also claims to "repair corrupted PDF (where possible)".
It turns out, where possible means, most of the time it is not possible. It failed to open the file with very minimal error message, let along repairing it. Since pdftk is GPL'ed, I thought I might be able to put more debugging information to figure out what exactly were wrong with these corrupted files. Then it turns out it is actually developed in Java and needs gcj to compile. Too much work to have the build environment set up -- so I gave up.
Update: I realised that publishing something like this is probably not good to the commercial companies behind some of these PDF repair software. I still have the content encrypted to me for my own reference.
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Update again: The said vendor has already fixed up their program to prevent copying out repaird PDF from evaluation version of the software. Good on them, and sorry I do not have a copy of older version of that program (thus no need to ask me about it).
So in the end I managed to repair those two corrupted PDF files and kept the client happy, using just evaluation version of a commercial software. And about making a crippled evaluation version -- there is little point crippling the application as there might be trivial ways getting around it. Cripple your output to annoy potential customers, and they might buy your software if they are desperate enough.