||WordStar is a Word Processor application originally published by MicroPro. WS4 files currently cannot by identified though a PRONOM identification signature.
On the surface it's a plain text file, however the format 'shifts' the last byte of each word. Effectively it is 'flipping' the first bit of the ASCII character from 0 to 1. so a lower case 'r' (hex value 0x72) becomes 'ò' (hex value 0xF2); lower case 'd' (hex 0x64) becomes 'ä' (hex 0xE4) and so on.
It should be possible to write a simple decoder application for WS4 files, however note that the conjecture above is based on observation of a limited pool of files, and there may be additional subtleties yet to be encountered and understood. Please contact the PRONOM team if you have any further information about this format.