You can already digitally sign documents in LibreOffice (including "qualified electronic signatures" issued by European countries). I would be surprised if you can't do it in Microsoft Office too.
However, qualified electronic signatures are harder to manage than what eIDAS simply calls "electronic signatures" (i.e. anything you put your name on): DocuSign value-add is a third-party to record an audit trail (time and date, IP address, assurance signatory has access to a particular email address...), basically, someone with no interest in misrepresenting facts about signatories to a document.
There's a lot of legislation around this too, and that can be costly.
