Hi folks When viewing some [not 'all'] PDFs I've created via T'bird's inbult PDF preview on my W10 Desktop PC an annoying black blob in the shape of a car key now appears on the PDF's pages from page 2 onwards. When viewing the same file via an iOS device or inside Dropbox there is no black blob. Also, when viewing the same file via the full Adobe Acrobat APP on my W10 Desktop PC there is no black blob. This black key-shape blob only shows inside T'bird's inbuilt PDF previewer. I know how to change the preview function inside Tbird to instead open any PDF in Acrobat, but as I quite like the T'bird PDF preview feature does anyone know why these black keys are appearing and how to get rid of them? '''Further info:''' The only PDFs with the black blobs are those created via my W10 Desktop PC's PowerPoint APP's "Save as Adobe PDF" function. There is no such black blob on the PowerPoint pages themselves, and again no blobs appear when viewing the new PDF on any iOS device or within Dropbox. Additonally, and since writing the above lines, I have emailed the PDF to a friend who has opened it on his W10 Laptop and there are NO [again, NONE] black blobs on his screen [he uses Outlook as his email handler]. Thus, I feel certain the problem is within T'bird's PDF preview code. Is there any fix for this? Thanks.