Add-in and edit word document in Add-in

Question

Hello every body.

I have to build an Shared Add-in project.

Add when I add this Add-in to Word, I should Edit Word document by it.

Ex: wher I select on a sentence or word in the document and then I press on Add-in button in Word, I should take selected sentence and make some proccessing on it using Add-in.

Can any body help me

Thanks