some pdfs i downloaded last year (most around 2000kb) open up in 9.1, sometimes, with a black sheen over the pages making them illegible, at other times, the black sheen is absent and the document can be read. but if i close the file and then try to open it a second time, the sheen appears. even with the sheen obliterating the pages, the navigation pane on the left of the screen shows the pages as clear. these pdfs are all 'open access', but my browser tags then as '(secured)'. i pay heavily for bandwidth so before i start downloading again, i'd be interested to hear if anyone has a fix for this. i've done virus scans, updates, and so forth.