The latest PDFNet.dll version works fine on most machines, but when I copy to a Windows Server 2008 machine I get the following error.
Could not load file or assembly 'PDFNet' or one of its dependencies. Strong name signature could not be verified. The assembly may have been tampered with, or it was delay signed but not fully signed with the correct private key. (Exception from HRESULT: 0x80131045)
And from the file properties it says it has an invalid digital signature.
The digital signature is not valid
As per Microsoft requirements starting in 2017 we code sign PDFNet using SHA256.
Windows Server 2008 SP2 does not included support for SHA256 and requires updating. See this MSDN KB article
Same error applies to Windows Vista SP2.