will downloading libre office interfere with MS office currently installed?
In my experience, it should not. But you will find that opening a document directly by double clicking on it in a list of files (My Documents, whatever) will open that document in the default application, which might not be the application you want to use. So, if you want to open a document using specifically LibreOffice, for example, first open the LO component (Writer, Calc etc) then use the Open menu item to browse to the file or document you want, and open it that way. Use the same procedure to open a document specifically in MS Office. Open the application first, then browse to the document you want open.
An alternative method is to right click on the document name in the list of files, select Open With… and choose LO. Or MS Office. Or something else, in the general case. A very handy way to open documents of all sorts.
no help here