Since updating to Adobe Acrobat XI Standard, when I open a PDF file for the first time, I can alter it and save it. But once I close it and then reopen it to change it, I cannot then save it again. I get the message "The document could not be saved. The file may be read-only, or another user may have it open." I can then save as, but only with a new name. Any ideas?
Any chance you use the preview pane in Windows Explorer?
It sounds like a temp file of the pdf is active. The message could be caused by another user actually having the file open, your system not cleaning out temp files after a pdf is closed, or something like having Explorer's preview pane displaying the pdf you want to edit and locking out saving in the process.