The reason that so many of us are suggesting the iPad is because it really IS the best tablet on the market, bar none, for the job.
Firstly, it has a 4:3 aspect ratio, which is much better for reading on than the 16:9 or 16:10 ratio found on most other tablets.
Secondly, the very high pixel density of the screen (double that of most of its rivals) makes text crisp and sharp.
Thirdly, there are some outstanding PDF reading and annotation apps available. The one that most people recommend is "Goodreader".
And yes, you can comfortably read an A4 page on it without having to zoom in and pan around.