I'm not a lawyer, this isn't legal advice, if you get sued for doing this you agree to indemnify me for any damages that arise from you following my advice and ignoring the "capitulate to all lawyers or hire one of your own" part.
That said.
The common standard for including the OGL is that it has to be easy to find and included with every copy that you send, though the preferred method is to make it accessible through the common interface for whatever the heck it is that you're sending. A seperate text file is accessable for some things (I used to do ZIP'd RTFs with the OGL as a text file), but not for others (In the PDFs that I do now, I include it in the the body of the document in a small font.)
So, to be safe, include it in the body of each .DOC or .PDF that you make. If you want to save space, however, you could put it in a seperate text file, but only if you bundle the DOCs and PDFs in some kind of archive file and it's clear what OGL goes with what document. (Though, theoretically, you could just lump them all together...)