Enable Extended Commenting in Acrobat Reader
If you are sending a PDF to a user who does not have Adobe Acrobat, and who will be using Acrobat Reader to view the PDF, you must enable the PDF so that they can add comments
1. Open the PDF you wish to send
2. Go to File > Save As… > Reader Extended PDF > click on Enable Commenting and Measuring…
3. A window will open warning you that in order to do this, some actions such as editing the document, will be restricted. Acrobat suggests that you save the Reader Enabled PDF as a version different from the original so you can go back and edit the original if necessary. Click Ok
4. In the Save As window, type the name of the new PDF and select a location to save it. Click Save
5. Now when the user opens the file in Reader they will be able to add the same kind of markup and annotation options as those available in Adobe Acrobat X
