[whpalmer4]

You can link or embed files in OmniFocus items by a number of means. One is to simply drag and drop the file into the note field; hold down the option key as you do so (a green circle with a white + will appear) if you want to embed a copy of the file, otherwise it will store a link to the file. Another route is to select the target action and choose Edit->Attach File... and similarly right-or-control-clicking to bring up the contextual menu and selecting Attach File...

What gets stored in the case of a link is just the name of the file, so if you move the file or rename it (or delete it), when you try to access the file through the link OmniFocus will put up a file chooser dialog and allow you to show it where the file has gone.

If you embed the file, a copy is made and stored in the OmniFocus database (you'll want to tread carefully if you do a lot of this and sync your database with an iPhone or iPad). You need to be careful if you want to edit the file because it will not sync your changes if you edit it in what would seem to be the most obvious way! If you want to edit the file, my advice is to make your changes, save the resulting file to your desktop as a new file, then embed the new file and remove the old one. If you need to edit the files frequently, you might be better off storing them in Dropbox and just keeping a reminder of where they are in OmniFocus.