How to create custom Rubber Stamp Annotation

Product: @pdftron/pdfnet-node

Product Version: 10.2.0

Please give a brief summary of your issue:
I’m trying to create a custom rubber stamp annotation but I don’t know how to instantiate the 3rd parameter of PDFNet.RubberStampAnnot.createCustom

Please provide a link to a minimal sample where the issue is reproducible: PDFTron pdfnet-node Class: RubberStampAnnot

Can you tell me what you want to achieve buy using createCustom with the form_xobject? I do believe a better option for you would be to use the Stamper class which allows you use custom images for the stamp and set the appearance via class properties. Examples for the Stamper class can be found here.