If IExplorer Proxy settings are greyed out, to reveal full URL to the PAC file via cmd input the following text:
reg query "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings"
Output:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
...
AutoConfigURL REG_SZ http://<full_path>/proxy.pac
...
Alternative method is to use Chrome browser and enable Debug to Disk: chrome://net-export/
By privilege15