I only use very basic macros, so this is a simple workaround.
You would need to type the keywords into the beginning of your document, then select the text. Then start recording macro. Copy the selected text, go to File, Properties, Summary, click in Keywords, Paste, OK, then stop macro. You could assign this a keyboard shortcut using Customize, Keyboard.
I think anything more high-powered would require some Visual Basic.
Cheers