This post was written by John Heckman: "Word 2003 and 2007 have a "feature" that creates a read-only copy of a document when you copy it to start a new document. This can sometimes be turned on without users being aware of it. In theory it is supposed to prompt you when you create the new document, but that doesn't always work. The net result is that users wind up with documents they can't edit and don't know why.
To turn off this feature in a given document, in Word 2003, go to Tools | Options | Security and uncheck the box that says "Read Only Recommended."
In Word 2007, Select "Save As" a Word document. When the Save box appears, click "Tools" at the bottom left corner, then General Options. Make sure the box "Read-Only Recommended" is NOT checked. Note that if you are using a document management system such as Worldox, you will have to exit out of the DMS in order to get the native Word 2007 save dialog to do this.
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Source: Does It Compute? 4 August 2010, reproduced with permission of the author.