I have to agree with how painfully slow it is at opening and turning pages in many pdfs.
I use mine to read various RPG books and the size of the pdf isn't the issue, it's the complexity of the page layout, art, etc.
As an example I have one game that is 100meg pdf of over 600 pages, this the reader handles no problem, it has a simple page layout and clean simple pictures.
A different game that is only a 7 meg pdf, the reader can't even open, it times out and crashed, this publisher uses complex page layouts, background images, etc, and all their products are effectively impossible to use on the dr1000.
Tbh it has been slightly disappointing, it is just about usable at home where all I want to do is read through a game book at a slow pace, as a usable item for using during game play when you need to be able to find information quickly it fails utterly
Hopefully things will improve as the software evolves, but at the moment it is a disappointing purchase.
Edit: Though I'd better add I have a Cybook Gen 3 that I've been using for a while now that I love and got used to how quickly it does normal page turns (never tried pdfs on it though) so perhaps I had an unrealistic viewpoint based upon how quick pdf pageturns are on my PC's, but waiting 10-20 secs for a page turn on the dr1000 feels like a lifetime.