The resource content must be located in the same to ImageGear assembly place.

A call to an Initialize() method should be paired with a call to the Terminate method. The very first call to Initialize() will initialize the entire PDF library, while its paired call to Terminate method will de-initialize and release its memory. You must not use or re-initialize PDF or PS after it has been terminated and its memory has been released in the main application thread. Multiple PDF initialization/termination will take place as a multi-threaded PDF application, because it is required to intialize and terminate PDF in each child thread.

PS support requires both ImGearFileFormats.Filters.Add(ImGearPDF.CreatePDFFormat()) and ImGearFileFormats.Filters.Add(ImGearPDF.CreatePSFormat()) calls be made before the call to ImGearPDF.Initialize().

Reference