Users searching for txt to srt conversion are usually looking for a way to manually create movie subtitles from a text file. Usually you can import .text files to any subtitle making program and save them in one of the supported file formats, including the most common SRT format. Plenty of subtitling programs exist for Windows and some worthwhile options are also on Apple Store for Mac users. There are even dedicated apps for Android available on Google Market.
Just keep in mind that simple text edits and changes (like typos, text encoding etc.) can be done using any text editor, you do not need dedicated subtitling software for that.
Open TXT file Open SRT fileA subtitle editor for GNOME
A program for editing of text subtitles for videos
Older subtitling program for Mac
A software for subtitle editing and preparation
Program for creating and managing movie subtitles