I am loving this device more and more, but I am going so slow that to get a proper review it would take me years

- so I thought I would go one step at a time.
As you know, you can choose which of two viewers to use for your files by pressing and holding the ok button (don't know how to replicate this with the stylus yet).
Adobeviewer:
Zoom button does work, and so does TTS. However, with the zoom button you lose pagination if you enlarge the page too much, the beginning and end of each line end up outside the viewable area. Also, without reflow a change in page moves to the next page, not to the next section in the same page there is a useful map of where you are in the page in the bottom left corner of the screen. Not so if you use the reflow, which at least for the files I could see works perfectly.
When the text rotates with the g-sensor, the effect is of zooming in but without reflow. However, if you do set the reflow before rotating the device, the effect is that if you then zoom in the page correctly, i.e. when page turning you move to the next section in the page, rather than to the corresponding portion (e.g. top part) on the next page.
The zoom submenu has more options that the Pdfviewer, and with the reflow option you can move from one section of the page to the next one flawlessly. As for annotation, you can call up the note function with the quick menu, but all you can do is select a portion of the text. You can also search inside a document. You cannot tap at the bottom of the page to navigate the document, but you can swipe the page to turn it (left to write goes back, right to left goes forward). You can add a bookmark by tapping on a corner of the page, and remove it doing the same.
Pdfviewer: works essentially like adobeviewer, with two main differences: there seems to be no possibility for TTS with this viewer, and when you change pages in reflow mode, as you turn the pages the new screen carries over the last line of the previous section, slightly underscored so that one does not lose track (while with adobeviewer you do not carry such last line along).
If you have zoomed but are not in reflow mode (e.g. if you have rotated the device), you can move from the top to the bottom part of a page by using the forward/backward buttons (either those on the side of the device, or those around the ok button all four directions work, but two are to move inside a page, while two are to move from one page to the next, while staying in the same portion e.g. moving from the top of page 3 to the top of page 4). With the Adobeviewer the system is less flexible, in that you have to use the ring around the OK button to go where you want. Here if you want to add a bookmark you have two options: if you use the quick menu, you only bookmark a page; if instead you tap in the right hand corner of the page, you also insert a tab.
EPUB files
You can use Adobeviewer for these files, too, and it all seem to work as for the pdf (save for the fact that you do not need reflow here!)