I have been trying to make comments in several PDF documents lately. The problem is that I have not known how to. At home I use Adobe Acrobat Reader 7.0 and I have read that it’s supposed to be possible to make comments using that software.
Today I found the solution. The original PDF have to be made in Adobe Acrobat 7.0 and it should be made available for commenting. If not available for commenting, you can only comment using Adobe Acrobat 7 (not reader: the free version).
For more information on this issue, visit PLANET PDF