To re-use the work of another, the format is important. It's difficult to make edits to a PDF file, and some older file extensions (e.g. .wps) can be difficult to use on modern computers.
Consider offering your text-based teaching materials in an accessible and editable format like Rich Text File (.rtf) or even a plain text file that can be read by a number of different software programs. An HTML file is a good option too.
Making a video for your class? Consider the format and the available players carefully. The .mp4 extension is often recommended for OER because of the many players that read it and its easy reuse for others.
Read more about File Formats for OER at the OER Handbook here.