• View PDF, PPt and Tiff online with Google Docs, even you do not have a Google Account or you do not want to login it. and you can embed the online documents into your own web pages.
• Google Docs add OCR support to PDF and Images, so you can OCR your scanned PDF, Fax, Images without any fee.
• Built-in PDF Reader for Google Chrome, view PDF just like view html. Chromium’s blog announced that the latest Google Chrome dev build for Windows and Mac includes a plug-in for viewing PDF files. The plug-in can be enabled by going to chrome://plugins/ and clicking on “Enable” for the “Chrome PDF Viewer” plug-in.
  When you click on a link to a PDF file, Chrome no longer opens the file using the Adobe Reader plug-in. Instead, Google Chrome uses a basic PDF viewer that lacks many useful features like pagination and bookmarks.

From now on, you can freely OCR your scan PDF documents, Images and Fax online with Google Docs.
When you upload files to Google Docs, you’ll notice a new option that tells Google to convert the text from PDF and image files to Google Docs documents. The feature has been released last year as an experiment, so Google had enough time to improve the accuracy of the results.
I’ve done some test and the result wasn’t great. About 10% of the text has been incorrectly converted and the formatting hasn’t been preserved.

“This document contains text automatically extracted from a PDF or image file. Formatting may have been lost and not all text may have been recognized,” explained Google in a note included in the document.
This feature only works for the following languages: English, French, Italian, German and Spanish. “For the technically curious: we’re using Optical Character Recognition (OCR) that our friends from Google Books helped us set up. OCR works best with high-resolution images, and not all formatting may be preserved.”, Google Docs Blog says.
btw, another good news, with Google Docs, you can freely view online PDF, PowerPoint and Tiff, without need to login your Google Account or download them, you can also embed them in your own web page. for details, please visit here.

Google Docs supports to upload and preview PDF, It can save PDF page as image, and I notice the default name is gview, and format is png, so I think it seems to base on GSView.

GSview is a graphical interface for Ghostscript.Ghostscript is an interpreter for the PostScript page description language used by laser printers.For documents following the Adobe PostScript Document Structuring Conventions, GSview allows selected pages to be viewed or printed.GSview requires
Ghostscript.GSview is available for Windows, OS/2 and Linux.