PF4Mobile,
I don't tell you to read PDFs on PC.
I don't read PDFs, I convert them to something suitable for reading.
Of course I don't think that reading on PC is good for anything.
Avoid reading on PC as much as possible. Certainly not books.
But if reading pdf is job-related and you have to work on your PC anyway...
Usually I have a pdf open on one monitor while something else on another and it is not convenient to involve also a reader at the same time.
Besides, work related PDFs are usually A4. And A4 on 9.7" screen is not easy to read.
If you read it fitted to the screen all at once - it is even worse for your eyes.
To zoom, reflow, scroll around? If you have no life.
If it is not job-related, you should not read PDFs at all! Ever!
Unless they are specifically generated for your reader and according to your preferences
In conclusion, I don't consider PDFs suitable for e-readers and do not acknowledge their existence
One exception:
Sheet music. I use a 9.7" reader sometimes for it. But it is a very specific task, not so hard on eyes.
Oh, one other thing. I wrote earlier that 6" reader must be white. Not to be a racist, I want to step back somewhat from that statement:
Of course, you can read in landscape mode. Then you can set margins 1 cm on both sides and have a proper 10 cm text line. With such wide margins a black reader could be acceptable.