[https://www.libreoffice.org/ LibreOffice] from the Document Foundation is a free office suite that is a suitable replacement for Microsoft Office. The software is free, and works on all platforms.
'''LibreOffice''' is able to read and write documents in Microsoft Office formats; enabling you to share your work with people using Microsoft Office. There isn't 100% "round-trip" compatibility between LibreOffice and Microsoft Office. LO has features that MO isn't capable of, and vice versa<ref>https://wiki.documentfoundation.org/Feature_Comparison:_LibreOffice_-_Microsoft_Office</ref>. So, in some settings you may be forced to purchase Microsoft Office. Beware that Microsoft Office isn't even compatible with itself if you compare the Windows version to the Mac version to the "rental" Office365 version.
LibreOffice also exports PDF documents with a single click; so if you simply want to publish a finished product, you can easily share a pdf file with others.