How can I use “Ctrl + Shift + V” to paste plain, non-formatted text, into a Word document?

Here are the steps:

• From the View tab, click on Macros -> View Macros
• In the Macros dialog, enter PasteSpecial in the macro name field and click Create.
• Replace the contents of the code editor with the following code:

Sub PasteSpecial()
On Error GoTo errHandler

        Selection.PasteSpecial DataType:=wdPasteText
        Exit Sub
    
errHandler:
        Selection.Paste
End Sub

• Save and close the code editor
• Go to File tab -> Options -> Customize Ribbon, click on the Customize... button after "keyboard shortcuts:"
• Choose Macro in the Categories box and choose PasteSpecial in the Macros box. In Press new shortcut key box, enter ctrl+shift+V, then click Assign.
• Click OK to close the Word Options dialog.

"Paste as plain text" – Universal macro which works with any application

This is AutoHotKey macro which will paste clipboard content as non-formatted text in any application which by default works with formatted text (Word, Excel, PowerPoint, Outlook, Write, you name it.)

Keyboard shortcut: Ctrl + Win + V

^#v::   ;work with clipboard: paste clipboard content as plain text
    ClipboardOld := ClipboardAll  ;save original clipboard contents
    Clipboard = %Clipboard%  ;store plain text from clipboard to clipboard
    Send ^v  ;send the Ctrl+V command
    Sleep, 250  ;give some time to finish paste (before restoring clipboard)
    Clipboard := ClipboardOld  ;restore the original clipboard contents
    ClipboardOld =  ;clear temporary variable (potentially contains large data)
    Return