A good format to share books which content is mainly text is the EPUB used for e-books.
The advantage of e-books is you can consult thousands of volumes in your shop without the need of a shelf.
EPUB readers are available for every type of smartphone, and the text flush smoothly in the small screens, oppositely to PDF which, being static like an image, often requires to jump from the start to the end of lines like playing a tennis match.
A good free EPUB generator, available for every operating system, is Calibre:
http://calibre-ebook.com/
The drawback is technical literature requires many images and tables, and these will not flush smoothly as text on small screens.
Oh, of course books have to be
typed, not just scanned!
Even the most sophisticated OCR software (the one you need to convert the graphical "profile" of letters into text) is not error-free, specially with old books. Often, for example, a lower case CL becomes a D (cl -> d) or vice-versa, and results could be dangerous, in mechanics (a cluster is far different from a duster!).
I noticed the time required for accurately checking a text for errors is not very shorter than that required to retype the same text, at least for fast typers.