What a visible signature shows and where: the page and rectangle of its widget, the text (by default the signer's name, the date, the reason and the location) and an optional image, such as a scanned handwritten signature.
public sealed class PdfSignatureAppearance
ISO 32000-2 §12.7.5.5 (a signature field's widget gives its position with Rect; signing updates the widget's AP),
§12.5.6.19 (widget annotations) and §12.5.5 (the appearance stream, a form XObject whose bounding box maps onto the rectangle).
The appearance is written before the byte range is computed, so the signature covers it.
With an image and text, the image takes the left two fifths of a rectangle wider than it is tall (the top half of a taller one) and the text the rest; the image keeps its aspect ratio, centred in its part. Text is shown one line per line of Text, at FontSize or, by default, at the largest size at which every line fits.
kind:method, kind:property, kind:ctor. Press Esc to clear.PdfSignatureAppearance(Int32, PdfRectangle)Initializes a new instance of the PdfSignatureAppearance class.FontGets or sets the font of the text, a font of the document being signed; null (the default) uses Helvetica, which shows WinAnsiEncoding text only. Use an embedded font for other text and for PDF/A.FontSizeGets or sets the font size in points, or null (the default) to size the text automatically: the largest size at which every line fits the text's part of the rectangle.ImageGets or sets the image shown beside the text, created by the document being signed, or null.PageIndexGets or sets the zero-based index of the page a new signature field's widget goes on. Signing a field that already exists keeps its widget's page and rectangle and draws the appearance there.RectangleGets or sets the rectangle of a new signature field's widget, in the page's default user space.TextGets or sets the text shown, one line per line; null (the default) shows Digitally signed by and the signer's name (SignerName, else the certificate's subject name), Date: and the signing time, and Reason: and Location: when the options give them. An empty string shows no text.