Translating a PDF documents with Google

Surprisingly the Google Docs Viewer (the page you see when you click "Quick View" from search results or a PDF attachment in Gmail) does not have translation built-in

You can of course copy and paste the text from the Google Docs Viewer into Google Translate by going to View > Plain HTML and selecting the text to translate. However the best way is pasting the PDF's URL into Google Translate's translation area (where you normally type the words to translate).

Note: the original PDF must have selectable text i.e. it must not be made-up of image files. If you have a small document of this type (e.g. one produced from a scanner) you could try upload it to Google Docs where you can request that Google tries to "read" it with OCR. See this page for more details of Google's OCR scanning limitations.