Good choice on going with LibreOffice, anywhere saying they'll give you MS Office for cheap are going to be installing pirated versions.
As for PDFs, if you mean word to pdf, you can do that in LibreOffice
If you mean PDF to word there is
https://www.pdftoword.com/ which is run by Nitro which is a reputable company (and a good option if you are looking to buy PDF software), but I still wouldn't put any sensitive documents through there since you are basically sending them to a third party