Google announced today A new feature in Gmail that allows you to easily view PDFs without having to install additional software.
Using existing technology in Google Docs and Google Book Search, users can quickly open PDF files simply by clicking on the "view" link, as it appears next to their respective attachments. If you need to view the PDF in HTML mode, click the "Plain HTML" link at the top of the new viewer.
Don't want to drop your software offline? Alright, click on the "download" link and download the file locally to your machine. This is also valid for anyone who wants to edit some information in the file, a property not available in the Google viewer.