here is what they say about this file in that doc :
Network Control File
The Paradox network control file, PDOXUSRS.NET, serves as the reference point for all lock files created by Paradox. The net file contains the users currently using the BDE and which table they're accessing. Each lock file references the network control file and contains information regarding the locks on the table and by which user, so each user must map to the same network control file in the same way, but not necessarily with the same drive letter.
For example, if you are using volume DATA on server SERVER_1 and the network control file is in the directory \PDOXDATA each user must map \\SERVER_1\DATA:\PDOXDATA the same way, however, each user should, but is not required to use the same drive letter. If the network you are using does not have volumes, then DATA would be a directory off the root of SERVER_1.
If you are mapping \\SERVER_1\DATA to the root of drive P: then each Paradox system would specify the location of PARADOX.NET as P:\PDOXDATA\. However, other users could map \\SERVER_1\DATA to the root of drive O: and specify O:\PDOXDATA\ as the location of the network control file.