So now the question - what is the downside of doing this?
I assume I will have to do this little set up everytime I upgrade the OS - but that is a very small price to pay.
This also seems to solve the other annoyance I had where the original file disappears (when using the method of holding the option key down) and one has to hit the "revert" button (or a name to that effect) to keep the original file.
I'm going to start to record the other annoyances with ElCapitan - maybe there are simple fixes like this one for those too.
I do use google - also did in this case but that was a while back when I first encountered this problem.
The only work-around at that time that came up was using the option key to change "Duplicate" to "Save As..."
The 'permanent fix' via the keyboard shortcut wasn't shown at that time - at least google didn't bring it up.
But regardless - I find that the advice/information I get here on ehMac is usually much better and more trustworthy than what google brings up
BTW; Did you get your original "read/write" permissions problem sorted out???
After I opened the pdf file with Acrobat I left it like that.
Just went back to try to open that pdf with Preview and it opened as if nothing had ever happened.
But I have seen similar behaviour with ElCapitan before - something doesn't work the way it should (and did before) and after one tries a work-a-round (assuming there is one), the problem suddenly disappears.
It seems a lot of code was rewritten and it's not as robust as the earlier versions of OS X.
Just had the same issue opening jpg images with Preview.
I had 26 images I as working on - 21 opened fine and suddenly the last 5 wouldn't open andgave a message that permissions were preventing the file from opening and to correct permissions.
Except that permissions were fine when I checked.
Those images also opened with every other image application I had.
Eventually I decided to close preview and launch it again - problem disappeared on all of the five problem images.