I had to force quit Pages as it was not responding (apparently my computer ran out of application memory and almost all applications stopped working).
After restarting (which involved force quitting all those applications including pages), some (but not all) of the files that were open in the previous session cannot be opened. The error message I get reads
"File" can't be opened right now.
Pages couldn't read the file.
The file exists and was apparently modified at a time after I worked on it last but well before the restart.
Is there a way to re-claim the file or at least the text in it?
Edit. It does not appear that the file is damaged, because even if I recover a previous version from backup, Pages cannot open that either (nor does it want to open a copy). So, it appears that the file is somehow locked.