It also depends on how the PDF is secured. In some cases, only the original author of the document can edit it. I assume that this will be the case for bank documents, at least we do it like this at our company for financial statements etc.
Hi! What kind of account is it? Personal or business? Also from UBS Switzerland AG, or UBS Europe SE or another UBS entity? and from where do you download this statement exactly? From the “Inbox” in the e-banking?
You can print the pdf to a pdf file and it should work.
You can also use pdftk if you’re not afraid of the command line in Unix.
You can also use gimp to edit the pdf.
But know that when you blacken things, it’s best to also “flatten” or rasterize the file afterwards because in some cases it just adds a black rectangle over the data but doesn’t actually cover it and it can be gotten back.
Or the simplest really is to print it out, blacken with a sharpie, scan again. Or print it out on paper, scan as an image, blacken on the computer, and save as png or jpg.