1.Does sdk provide Blank page and duplicate page?
Yes, to add a blank
`
doc.PagePushBack(doc.PageCreate());
`
As for duplicating, there is no direct way, but the easiest would be the following.
`
Page duplicate = doc.PageCreate(source_page.GetCropBox());
doc.PagePushBack(duplicate);
Stamper stamper = new Stamper(Stamper.SizeType.e_relative_scale, 1.0, 1.0);
stamper.StampPage(doc, source_page, new PageSet(doc.GetPageCount()));
`
See following samples for more.
https://www.pdftron.com/pdfnet/samplecode.html#PDFPage