When you save, Paint.NET first writes the data to a ".pdnSave" file. Then, it renames the original file to ".pdnBak", and renames the ".pdnSave" file to original file name. Then it deletes the ".pdnBak" file. With this procedure, if there's an error/crash while saving, it won't overwrite/corrupt/destroy the original file contents.    If you still have "pdnbak" files getting littered around, then most likely you have an over-anxious antivirus scanner which is locking those files and preventing