First, you are thinking of uncompressed TIF files. Compressed they are usually within about 1% +/- of the PDF of the same data. JPG's are the worst possible choice for drawings and text. Because every time that you save one, you usually lose a little. Anyone willing to spend the money or "steal" or legally acquire the necessary software can edit a PDF file in the sense that you mean. But I have been in the business of scanning and reprinting vintage military technical manuals for nearly 20 years and doing it the hard way for more than 20 years before that. You cannot edit a PDF file in the sense that I mean. In order to do it, you must first convert it to a different suitable file type, which for scanned text and drawings (which covers about 98% of all of the manuals that we are concerned with here) will be B&W TIF. Then you can clean it up so that it looks new, crisp, clean, nothing but black on white, etc. and when you are finished, convert it back to a smaller PDF or print it as hard copy for actual use.