The Zoho Viewer API lets anyone enable viewing office documents online using just the web browser. The supported file formats are listed here.
To get started with the Zoho Viewer API, you would first need to get an API key for your needs. You can get the API key by filling in the form at http://writer.zoho.com/apikey.htm. You will need to use this key in all your API calls.
Here are the APIs available in Zoho Viewer.