Originally Posted by NLight95
Is it because it's not formatted for e-book devices and there are many text reflow issues?
I'm thinking about converting any PDFs I have over to ePub.
Fundamentally yes. The whole point about PDF technology is that it is intended that the originator completely controls the layout and the end-user cannot change that.
If you have a PDF that:
a) was formatted for exactly the resolution of your device
b) you are not interested in ever changing the font size
then a PDF file can be OK for an e-reader.
However the vast majority of existing PDF files will break down on assumption a) and for most users assumption b) is one of the features they like to be able to use on an ebook.
Having said that, conversion from PDF to a format more suitable to ebooks can be a bit hit-and-miss both in terms of making sure the content transfers over correctly and even more so in terms of any formatting. Therefore despite the fact that it is not the ideal format for an ebook there might still be times it is the best you are going to get for a particular book that you already have available only in PDF format.