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You can use a batch sequence (aka Action). In the Output Options, you can choose a file prefix and/or suffix, though there are numerous utilities available, just google: batch rename files
In my opinion, open Action wizard and simply save them to PDF without adding any actions. And while saving them, add the suffix.
Please Note: It may change the property of Reader Extended files and similar.....
To do this:
Click File Menu-> Action Wizard-> Create new Action and do as shown in the screen shot below: