Only in the last few days, when I amend a pdf file with multiple pages, some characters are replaced with tofu boxes. All fonts have been embedded on creation and it has worked perfectly until the last week. Now, whenever I change something and save the file the tofu boxes appear. I have run a fix using the preflight / embed missing fonts / analyze and fix which does get rid of the tofu boxes, but it then makes all hidden layers appear! Help! Adobe Acrobat Pro on Windows 11.