If I download LibreOffice, will I lose any files or documents
No - you dont lose anything!
I don’t understand why ppl would ask questions like this.
Yes bobby, every one.
As soon as the first byte of the download touches your hard-disk it becomes a search&destroy nanobot that ravages each & every file upon that disk until all are shredded beyond redemption. In fact, this is the major feature of LibreOffice and why so many people download it each day.