One of the valuable and productivity-enhancing features in the Dreamweaver Document window is that the Design view (or the Design side of the Split view) serves as a functional word processor. You can compose text here using a standard set of editing tools as you type.
That said, it is more likely you'll copy text content from web pages or word processor documents.
Depending on the source of the text, Dreamweaver offers a set of options for pasting text into the Document window. These are accessed by choosing Edit | Paste Special. Use trial-and-error to find the option (ranging from minimalist Text Only to options that retain more formatting) that does the best job of pasting copied text into the Document window.