.ASCII File Extension Windows user? Open any file with File Viewer Lite File TypeASCII Text File DeveloperN/A Popularity 3.0 (2 Votes) Thanks for voting! Rare Uncommon Average Common Very Common CategoryText Files FormatText X Text This file is saved in a plain text format. You can open and view the contents of this file using a text editor. Definition Plain text file that uses ASCII encoding that can be opened and edited with any text editor; much more commonly uses the .ASC or .TXT extension. Program(s) that open .ASCII files Windows Any text editor Mac OS Any text editor Linux Any text editor Updated 8/11/2011 Need to open a .ASCII file? Try File Viewer Lite.