When i get pdf docs by mail, I always hesitate to open it as it is slow and a major pain in the ass. I sometimes wanna just browse through the document, rather than downloading it. Now what Google did is, they gave a "View" option near to the Download option. It looks like this:

Clicking "View" quickly opens the PDF inside your browser(not with Adobe Reader), complete with the graphics and formatting you expect to see in a PDF. It is the same feature used in Google Docs. Now at this stage, you can even view the document in html format, or download it or print the whole thing. Here.. take a look:

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