That signature is implemented as a AcroForm, so you should enable AcroForm engine to drawing that signature (and other forms, such as textfields or comboboxes, too).

You have three options to do that:
1. Recomended way #1
You may load document through pdfViewer1.Load(...) method. A lot of actions are performed inside this method and AcroForm initialisation is one of them. You can find more details in source code of PdfViewer: https://github.com/Patag...blob/master/PdfViewer.cs


2. Recomended Way #2
if it is not possible to use pdfViewer.Load method (due to mvvc limitations), then you should load document yourself in proper way. It is easy, just use following: PdfDocument.Load(path, new PdfForm()); In this case the forms engine will be enabled.


3. Way #3
You can use this way if you do not need to interact with AcroForms, but just drawing forms.
In this case you may set PdfViewer.RenderFlags property to FPDF_ANNOT.
Please note, you should not do this in the first and second cases.