//Get Default appearance for the control
string da = GetDefaultAppearance(doc.FormFill.InterForm, ctrl.Field.Dictionary);

//Parse DA
float[] strokeColor, fillColor;
float fs;
FS_MATRIX m;
string tagName;
Pdfium.FPDFTOOLS_ParseDefaultAppearance(da, out strokeColor, out fillColor, out tagName, out fs, out m);

//Check acroforms dictionary for the tagName
var font = doc.FormFill.InterForm.Fonts[tagName];


internal string GetDefaultAppearance(PdfInteractiveForms InterForms, PdfTypeDictionary dict = null, int level = 0, bool checkAcroFormsDictionary = true)
{
	if ((level > 128))
		return "";
	if (dict.ContainsKey("DA") && dict["DA"].Is<PdfTypeString>())
		return dict["DA"].As<PdfTypeString>().UnicodeString;
	if (dict.ContainsKey("Parent") && dict["Parent"].Is<PdfTypeDictionary>())
		return GetDefaultAppearance(InterForms, dict["Parent"].As<PdfTypeDictionary>(), level++);
	if (checkAcroFormsDictionary && InterForms.Dictionary != null && InterForms.Dictionary.ContainsKey("DA") && InterForms.Dictionary["DA"].Is<PdfTypeString>())
		return this.InterForms.Dictionary["DA"].As<PdfTypeString>().UnicodeString;
	return "";
}