As messages are entered directly into the computer, by the author or by a typist from the original. During layout, messages can be edited, rearranged, ordered into categories, deleted, etc.
Special software enables word processing.
Choose one that is well known. Training in its use may be needed. If you are thinking about making use of borrowed computers and of volunteers typists, it is important to have software that can convert documents from different types of word processing software. Some volunteers may type much more willingly, and accurately, if they are using software with which they are familiar.