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Theoretically it can be done, but it will be a challenge and a lot of work.

It is trivial to search through text files, in the link you provided (the dictionary) we used the 'grep' utility to search an ASCII file.
However searching through binary files is not so trivial. A the PRS-500/5 supports a good number of binary files. You will need to read the file and know how to handle the binary encoding. Usually this requires writing much software and require the developer to be familiar with the binary structure. Sometimes API are provided that do reduce the amount of knowledge the developer must have in order to read through the file.

At this point you can do a search. In addition some files are compressed text such as ePub that is a zipped HTML, but may also include images (binary).


So the binary files you wold have to read are (may be missing some)
PDF, RTF, LRF, LRX,
Compressed HTML(text) and images
EPUB

You might want to first start with ASCII(text) files then slowly start adding binaries to your search program. I'd recommend the next file after the txt be either EPUB or RTF.

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