[bonoboTP]

Yes, but not all documents are trivial to convert to a text file because the layout can be quite complex. A PDF file can have little bits of text floating anywhere and when you search inside the file, you can see it highlighted at its actual position.

[zo1]

I've had to work with PDF files before, and they're absolutely horrible. Precisely because of what you state: "little bits of text floating anywhere". Or something like disjoint, not-grouped, lines for table drawing, instead of a generic table with formatting, width/height, etc.

Though, I generally agree with you, PDF/A is quite a good way of storing documents for long-term. But, that doesn't mean that PNG files along with text files, even with x:y coordinates next to the pieces of text, aren't a feasible alternative.