Want a browser that tells sites it's a bot

After getting lots of search hits into documents that the sites want me to pay to view, I had an idea: Why not tell the site that I'm a Google bot? That's how Google got the full text of the document in the first place, no? Because the site saw it was a Google bot and gave it full access?

Does anyone know of a browser that lets you set the user-agent header to make sites think it's a bot/different browser?