Having evaluated lots of open source and commercially available products we have found the Aspose suite of components the most easily adoptable and feature rich SDKs that we have found to date.

We use the components to transform office documents into PDF / Images for further processing through our systems, however the Aspose Total suite offers a whole load of additional functionality that would have otherwise taken a lot of time / cost to develop.  Adopting the Aspose components means that we can quickly add functionally to out solution due to the ease and simplicity of the API design and developer documentation.  

I would highly recommend these components to others