Until now, whenever you received a message with PDF attachement, Gmail converted PDF files to HTML and removed images, and offered you to either download the original attachement or view as HTML. Now, Gmail has a new option that’ll show “View" link next to PDF attachments to let you view the PDF file without installing a PDF viewer like Adobe Reader. Clicking "View" quickly opens the PDF inside your browser, complete withThe new option uses the PDF viewer from Google Docs, which lets you zoom and search inside the (first 100 pages of the) file.
If you want, you can still view in plain HTML from a link at the top of the new viewer. And if you want to download, save, and view your PDFs later while offline using client software, you can still do that by hitting the "Download" link.