SW EPDM web client is like the normal EPDM client. The only difference which I see is , using web client you can have access of your data from anywhere if you are connected to your domain server. There is no special permission settings for web client. The folder permissions set to a group or a user would allow or dis allow from accessing files in a folder.
There is no feature available to show or hide a file of particular extension in EPDM.
If you want to show pdf files only, what you can do as a work around is create two different folders one for your CAD parts ,assemblies ,drawings,jpeg, doc etc and one folder for pdf files only.
Now with permission settings you can hide the folder with CAD data and show the folder with pdf files.