Someone sent you a link to a document published in Google Docs. You have the permission to view the document, but not edit it. Google doesn’t provide any option to copy the document to your account, where you can edit and play with it. Now Google OS reveals how to do that.
You can create a duplicate for the document by replacing:
http://docs.google.com/View?docid=AAAAA
With
http://docs.google.com/DocAction?action=copy&docid=AAAAA
(note: AAAAA is the document ID)
To simplify the whole process, there is a greasemonkey script, which adds a neat “Copy to my account” link below the document. I just tried it and it works like a charm! Once it’s copied to your account, you have full permission to modify it, whichever way you like… :|