Verify the following conditions are true:
MyCompany:OEM:1234, then you would call
PDFNet.Initializeonce, on the main thread.
PDFNet.Terminate, this is very rarely needed.
PDFNet.Initializebefore any other calls to PDFNet functions or constructors.
Finally, if the above doesn't help, then the key might not be compatible with the version of PDFNet you are trying, so download the latest version of PDFNet and try that one. http://www.pdftron.com/pdfnet/downloads.html
To see which OS/platform your license is for, in your license key you will see a string such as
::IAR:AMS(20160509): The letters
R are the platforms in this example.
Below are some of the most common.
W - Windows L - Linux M - Mac I - iOS A - Android B - Web (PDFNetJS)