A little more info, please.
Windows locks files based on their names. It has a fairly unfriendly way of doing so, which is why you have to reboot whenever certain executables/DLLs are updated. Linux/Unix looks at files based on inodes, which allows you to actually delete a file while someone else it writing to it without disaster (though it's not a habit I encourage).
Normally, PDF's are read and would be sharable. Only if you're talking about a user updating the PDF would I normally consider locking it. MS-WORD docs are different. A
WORD doc can be opened read-only, but it requires a deliberate effort.
Anyway, I haven't looked at that kind of problem, so I can't give a definite solution. I recommend that you check the Samba docs, since it's Samba's job to emulate the networked Windows filesystem, and I think I may recall seeing something about such issues there.
Unix often uses the concept of a
lockfile. This is simply a zero-length file whose mere presence is enough to indicate that a resource is locked. It's possible that Samba might even use this as part of whatever file-locking scheme they might be using. Unfortunately, lockfiles have to be explicitly created and destroyed, so if Samba intercepted an SMB file open/close operation, it could take that action as part of its network support functions, but a simple Unix/Linux file open/close can't.
