add document failed

[vastAndHazyAreamer]

I always fail to add STEPCAFCControl_Ceader_1 to the document. What is the reason?

[Ruud-DRS]

The if (readStatus != oc.IFSelect_ReturnStatus.IFSelect_RetDone) { statement checks if reading has failed, while in the code you print "read step success".
You also unlink the file before calling the transfer method. I think you need to unlink it after you called the transfer method.