To add a link to a recently used file:
Click or tap at the spot would like to insert the link in your document.
Go to Insert and select the drop arrow to the right of Link.
Select the file to insert from the list. If you don't see the file you want, select Insert Link and navigate to the file you want.
Note: Only files stored in OneDrive or SharePoint will be shown on the link gallery.
To create a custom link, type and select the link text and then continue from step 2 above. The selected text becomes a hyperlink to the related file.