[Hoff]

Wait a moment - isn't this the difference between "attaching" a file and "embedding" a file?

According to the help file:

"By default, OmniFocus creates links to the files you attach, rather than adding the files to your OmniFocus database. This keeps your database from growing needlessly (which is especially important if you are syncing your data), but the link will break if you delete the file or put it somewhere OmniFocus can’t find it. To make OmniFocus copy a file into its database for safekeeping, hold the Option key as you drop the file, or select Embed the file in the document in the Attach File dialog."