[wallcraft]

If you want to preserve the DRM (encryption) then your only choice is Adobe lending library ebooks. There are a very few ePubs, but most are PDFs. I suggest you try a few library PDFs to see if they are acceptable.

If not, then you will have to strip the DRM, either from the Adobe PDF or from the MOBI. This may be illegal in the US, particularly for lending library ebooks (where the personal use argument is less compelling than for ebooks you bought). You will have a better chance of format shifting the MOBI to LRF or ePub than the PDF, but most libraries have fewer MOBIs than PDFs.