[Quoth]

I should have looked at the short manual leaflet!
The two big buttons on either side are identical and are each two buttons, a prior and next for pages or items.

There seems to be no way to select internal links, so no hyperlinked footnotes, though there is a menu option called "set link".

There are bookmarks and one favourite category.

There is a white text on black mode which isn't sensible without a front or backlight. It suits OLED best though some are fans of it on LCD and eInk.

The supported picture (image) formats are in the manual, but no indication of size. It also claims to do 3 generations of Mobipocket: pdb (Palm), prc and mobi (Initial Kindle format as Amazon bought Mobipocket 2 years earlier). The Djvu is normally for scanned material as PDF alternative, so that and PDF unlikely to work well. Epub is maybe using the Adobe ADE package as there is a Digital Editions directory. Also claims to support RTF, Chm (MS Help?) and FB2.