I downloaded the pdf reader update again (using the above link I posted) and this time had it unpacked and the 2 files -"onyx_pdf_reader" and "update.oar"- transfered again to my M92 this way after connecting the device to my laptop: "Copy to" > "books (G)".
(I guess that is what you meant by "copy/paste to the reader's main memory via the usb cable.")
I did disconnect it from my pc afterwards. But on my M92 I still do not see where the "update.oar file" is, let alone both files to remove them.
Thank you too.
I think at this stage I better not even try to get into "beta" versions...