You can download clean, safe copies of your licensed Office version to burn to disk (.iso) or run .exe from Microsoft which can be activated with the Product Key you originally bought with it or audited using Belarc from Step 2 above. A good free compatible alternative to Office is ...
Installing Office is pretty much the same. If the new PC came with a trial version, uninstall that first. Then install Office from your disc. If you run into a problem, you’ll be directed to call Microsoft. You actually get three licenses with the retail version, so it may be awhile...