"The document could not be saved" - Preview error

I have the issue on macOS Sierra(10.12.1) and still have it on High Sierra(10.13.3).

I get this error message(not all the time) a lot after editing an image, and trying to save it. I can't quit Preview either, so the only way to close Preview for me when this happens is to force quit Preview.

Clicking on duplicate doesn't work because my edits made to the original document don't carry over and Preview still doesn't quit.

I realised this is a bug in the Mask tool. Remove the mask and the image saves without any problem. Avoid this tool until Apple addresses the issue. Checked on High Sierra 10.13.4.

A solution to this is to take a screenshot of the image preview before saving it(solution from @gpbl).

I was facing the same issue, I finally got the issue resolved by following steps:

1. Go to File
2. Click option 'Export as pdf'
3. Save the file name with pdf extension (like 'file_name.pdf')

This worked for me, so give it a try.