Word lets you translate an entire document in one go, either right click anywhere in the document, right click and select Translate, or go to Review | Translate | Translate Document.
As with translating a selection, the Translator will open in a sidebar, where you can select the languages to translate from and to.
Generally, Word will detect the language of the original text, but if not, select the From language. Then select the language you want to translate into.
Once you have selected the languages, click Translate. In this case, a separate document will open containing the translation. You can then save this document or do whatever you wish with the text in it.
Translation is a Microsoft online service. Anything translated is sent to Microsoft’s computers where it can be saved and shared without your knowledge. Government agencies can have access to the translated text, with or without a warrant.