PAC files are enabled in web browsers by entering the PAC file URL in the proxy connection settings, or by using the Web Proxy Auto-Discovery (WPAD) protocol. When executed, a PAC file returns a string with one or more proxy server URLs. PAC files are typically hosted on a web server and are named proxy.pac.
Since PAC files contain the configuration in plain text. You can use a text editor, such as Microsoft Notepad or Apple TextEdit to view or modify the files.
NOTE: The PAC file format was originally released in 1996 for use by Netscape Navigator 2.0.