This article explores different file formats that use the ACT file extension. It explains what each file type is, how to open each type, and how to convert your file to a different file format (if possible).

A file with the ACT file extension is an Adobe Color Table file (also called a Color Lookup Table file) used by Adobe Photoshop to store a collection of predefined colors. When saving an image for web publishing, you can add or remove colors to favor a higher quality image or a smaller file size.

If not used with Photoshop, you can have an ADPCM compressed audio file instead. These are used by some MP3 players and voice recorders which compress the audio using Adaptive Differential Pulse Code Modulation.

Alma CAD/CAM documents also use the ACT file extension. These store instructions that 3D cutting machines use to understand how to cut something.