Is not possible to sign a document with embedded signature

Technical Support Apryse SDK
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While there are a few ways to add an “invisible” signature, some of these ways might not work as intended with different PDF tools.

The best, most compliant, way to add a signature that is not visible is to add an Author/Certification signature, which can be thought of as a document wide signature added by the original document author. These can have be given a widget on page 1 with zero width and height, and no appearance. Other PDF readers should treat this as you expect.

Note, there can only be one author/certification signature, and it must be the first signature.

See the CertifyPDF function in the following sample, and just change the following line of code

SignatureWidget widgetAnnot = SignatureWidget.Create(doc, new Rect(143, 287, 219, 306), certification_sig_field);

to

SignatureWidget widgetAnnot = SignatureWidget.Create(doc, new Rect(0, 0, 0, 0), certification_sig_field);

and comment out this part

// (OPTIONAL) Add an appearance to the signature field.
Image img = Image.Create(doc, in_appearance_image_path);
widgetAnnot.CreateSignatureAppearance(img);
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