There are 4 file types use the .PAC file extension:
1. PAC Subtitles File
Proprietary subtitles format created by Screen Subtitling Systems; used for synchronizing closed captions with a video timeline; can be edited with subtitle editing software such as EZTitles and converted to more standard formats, including .SRT and .SUB.
Updated: October 8, 2017
2. Proxy Auto-Config File
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.
Updated: May 11, 2019
3. SBStudio II Song File
Song format, called a PAC or package file, used by SBStudio; made up of data blocks that store song information and audio data.
Updated: September 21, 2009
4. STAD Graphic File
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.
Updated: September 3, 2009