A pdf file, especially the one formatted for A4 or Letter page, is not a good format for majority of e-book reading devices.
You could make pdf file usable with an e-ink reading device if you prepare pdf file for page size 90x120mm.
Have a look at our wiki at various devices.
There are file formats that are better suited for use on portable reading devices. Formats such as epub, mobi, lit. For more information see:
https://wiki.mobileread.com/wiki/E-book_formats
For creating / converting have a look at Calibre software. It has nice GUI and also powerful commandline tools for batch comversion.
Have a look at other e-book publishers what formats THEY are using. Have a look a Baen - a DRM free, very polular and successful e-book publisher. Have a look at Fictionwise