Invalid annotation object error in PDFs

If you used Adobe acrobat to annotate a PDF file and you had Acrobat crashed or had to restart the computer abruptly during the annotation process then you might experience this problem when you reopen the PDF file from Acrobat. Of course if you use Skim or Preview to open the file then you will not get this popup window and everything will display without a problem. To solve this problem first open the PDF under consideration in Preview and then do a save as for the file. You can give the same file name and replace the file. Now everything will work fine.