If your process is running as 64bit, then you need the 64bit PDFNet.dll, and 64bit VC++ 2010 redistributables.
If you are still using the PDFNetLoader.dll assemlby, then remove that reference and any related code (typically single static call), and just reference PDFNet.dll normally.
If none of that helps can you post all the diagnostic information that you can.
If you can run SysInternals ProcessMonitor that is also useful in finding out why an assembly is not loading, since .Net will access the filesystem, but it might be that you can't run ProcessMonitor on Azure.