Why can't I edit a document when it opens in my browser?

There are chances that your browser swallowed the running application.

If you click on a document in TeamForge (for example, a Word doc), and it opens in your browser instead of launching a separate MS Word window, chances are you will not be able to edit this document. This is because your browser has either called one of the MS document viewers that do not have native edit capabilities, or the browser has 'swallowed' the running MS Word process and the document has written to your %TEMP% directory as a read-only file.

You can either choose to download the file to your desktop and then click on it to edit, or configure your browser to not swallow the application (this is described in various MS KB articles).