A PAC file is a configuration file used by web browsers to select an appropriate proxy server. It contains one or more JavaScript functions with one of them named FindProxyForURL, which defines rules for choosing a proxy server based on a given URL. PAC files are used for controlling and load-balancing Internet traffic, especially in corporate environments.

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.

Song format, called a PAC or package file, used by SBStudio; made up of data blocks that store song information and audio data.

Image format used by the STAD program for Atari ST systems; saved as a black and white image with a resolution of 640x400 pixels; considered a high-resolution graphic for Atari computers.