64 bit PDFNet.dll works fine from a Website ASP.NET project but when attempting to use the publish feature with the pre-compilation option you may get the following error:

Could not load file or assembly 'PDFNet' or one of its dependencies. An attempt was made to load a program with an incorrect format. WebSite ASPNETCOMPILER 0"

Getting the 64 bit PDFNet.dll to successfully publish with “Precompile during publishing” option enabled requires adding the following to publish profile in the App_Data folder:

<AspnetCompilerPath>C:\Windows\Microsoft.NET\Framework64\v4.0.30319</AspnetCompilerPath>