I work on combining a lot of different documents for proposal books in an answer to an RFP. Every now and then (randomly), some pages of the document - random letters will go invisible. They won't be gone, I say invisible because I found a hack, where I can select all the text, make it bold and then unbold, and all the letters show back up. Sometimes the text will come back all by itself in a day or two, but usually don't wait that long.
Here are a couple of screenshots I took from my recent book that had this issue:
This is a really big pain for larger books and when it's crunch time to get it submitted and I have to go back over every page and make sure all the right words/letters are there. I've struggled to find this issue anywhere online, I've uninstalled and reinstalled it, and tried looking through a Preflight report to no avail. If anyone has any advice/suggestions - I'd be happy to try!
Hope you are doing well and sorry for the trouble.
Would you mind sharing the version of the OS and the application you are using? To check the version of the application go to Help > About Acrobat and make sure you have the recent version 22.1.20142 installed. Go to Help > Check for updates and reboot the computer once.
Also try to repair the installation from the help menu (Win Only) and check
Is this an issue with a particular ODF file or with all the PDFs? Please try with a different PDF file and check. If the file is stored on a shared network/drive please download it to your computer locally and check.