A family of Microsoft word processing software products for creating web, email, and print documents.
Hi Chika,
Yes, you can e-sign a Word file in desktop Word for Windows. (I'll have to leave it to our Mac experts to say whether it's also available and what the process is.)
The start of the procedure is to click File > Info > Protect Document > Add a Digital Singature.
That leads to the following dialog.
In articles on the Internet, this type of signature is often called an "invisible digital signature" to distinguish it from the signature line type that Mia described, which is confusingly called a "digital signature" (of course, everything in Word is digital).
For illustrated steps and a video, see Add an Invisible Digital Signature To a Microsoft Word Document .