Hi Hilde,

Thanks for your question. Many things can cause this here are some examples:
1. The document is signed (marked by a yellow/gold lock in the document list in Projectplace)
2. The document is locked (marked by a grey lock in the document list in Projectplace)
3. The reviewer is not a member of the project. Non-members can participate in document reviews and enter comments but can not edit the document.
4. The reviewer is a member but part of a group that does not have write access to the folder where the document is.
5. The reviewer does not have write access to the temp files on her or his computer.
6. The reviewer does not have the appropriate application for editing the document and it opens in a viewer instead.

I hope one of these answers will help you, if not please let me know some more detail of the problem and I will try to help you further.

Best regards,
Karolina