Hi,
By default, the item security is applied on item related file.
You can check Item security settings via:
Tools->administration, Items tab, Security...
Here you are able to configure item security for each user.
If you want to check why the file has been locked, you can check the file's security via:
1. Select the file,
2. File menu->Properties...
3. Security tab.
If this file is locked by item, it should be "System or overridden security", and the Access Control List is the same with your item security setting.
Not sure if I fully understand your question, but hope this helps.
Thanks,
-Dicky
Dicky Shu
SQA Engineer
PSEB-GE-ACRD PSEB
Autodesk, Inc.