After installing LibreOffice some .doc files opened in MS Word no longer render correctly. They rendered OK before I installed LibreOffice. They render fine in LibreOffice Writer, but I’m not quite ready to switch yet. I uninstalled LibreOffice and it still doesn’t render correctly in MS Word. After MS Office repair the same problem occurs. This happened on two different machines.
MS Office 2016 Pro Plus 64bit (compatibility mode)
LibreOffice 5.4.1 64bit
LibreOffice does not alter MS Office installation in any way. Absolutely. It might change OS file types associations (if user chooses so at install time), but it neither changes (add/replace/remove) files related to MS Office, nor its data in registry. You may check the installer (MSI) for its actions (requires some competence in the technology, but nothing is hidden), or even source code (naturally available open-source on our repository, as everything related to LibreOffice).
But if you open a .doc in Writer, save it, and after that open it in Word, it’s possible that LO introduced some problems into the file - the format is foreign to LibreOffice, and its support is not ideal. It’s recommended to use ODF for working in LibreOffice, and only use foreign formats for exchange when required, always keeping latest version of the document as native ODF.
I’m speculating that some recent updates to MS Office might have broken the compatibility with older .doc files crafted as forms in earlier versions of MS Word.