I am running Adobe Acrobat Pro version 18.011.20040 on macOS Sierra 10.12.6. I am able to edit and save other documents, but this particular one prompts the error message "The document could not be saved. The file may be read-only, or another user may have it open. Please save the document with a different name or in a different folder". I have tried renaming and resaving but get the error message every time. I have edited this document before with no problems. The only discussions I have seen this question asked and answered many times for Windows devices but not on the Mac. Does anyone know how to fix this issue?
Have you checked the file is not set as read-only, under the file properties?