I've read that kindle can be dodgy when trying to download files that were NOT purchased from Amazon? I have downloaded thousands of pdf books
The built-in Kindle pdf reading app is very limited and not suitable for academic papers or text books, because it doesn't have an smart reflow option.
If you're on a budget and like the Amazon ecosystem, you could buy an older model, jail-break it and install the free KOReader app, which offers better PDF display options. (Note that this will work only with the first generation Kindle Paperwhite model and other older Kindle models.)
There are some large screen eInk readers suitable for reading .pdf files, however, they tend to be more expensive than more powerful tablets with same screen size.
IMHO, the best e-readers for .pdf files are tablets with a screen size of at least 10".
amazon kindle provides you support for PDF as well as their .azw format. If we go in detail:
support by them is for : Kindle Format 8 (AZW3), Kindle (AZW), TXT, PDF, unprotected MOBI, PRC natively; HTML DOC, DOCX, JPEG, GIF, PNG, PMP through conversion. amazon comes with less memory expansion.
However, they are for DRM protected files. So, You can buy other e-book readers if you want more support. I use barnes and nobles Nook reader. However, it is also somewhat like amazon when it comes to pdf it fails to load some scanned pdfs. for epub files its best.Nook comes with 32gb memory expansion.
I would still prefer amazon over nook. as most of my files are in PDF format. however, whatever device you get, do download format converter softwar