When installing LibreOffice, does it overwrite OpenOffice, or do I have to uninstall OpenOffice after installing LibreOffice? And in either case, are my OpenOffice documents saved?

I don’t know if LibreOffice recognizes my OpenOffice and overwrites it, or whether there is no relation between the two programs. I assume LibreOffice can read my OpenOffice documents.

Refer this question / answer. You documents will remain unaffected.