This seems to be a recent change: Google Translate can now be used to translate PDF files and Microsoft Office documents. Google first converts the document to the HTML format and then it displays the translated HTML file.
The nice thing is that Google converts the documents on the fly even if they haven't been indexed by Google. Just paste the address of a document in Google Translate's textarea and wait until the translation shows up. Unfortunately, the service is not well-suited for long documents: it only translated the first 9 pages of a PDF file.