C# equivalent of your code is
class Imagedata : PDFStreamEngine
{
// C# uses "base" keyword whenever Java uses "super"
// so instead of super(...) in Java we should call its C# equivalent (base):
public Imagedata()
: base(ResourceLoader.loadProperties("org/apache/pdfbox/resources/PDFTextStripper.properties", true))
{ }
// Java methods are virtual by default, when C# methods aren't.
// So we should be sure that processOperator method in base class
// (that is PDFStreamEngine)
// declared as "virtual"
protected override void processOperator(PDFOperator operations, List arguments)
{
base.processOperator(operations, arguments);
}
}