In a newly created document the value of this property is null. If the value has not been set when the document is saved (and for fields, the owner field has been added to GrapeCity.Documents.Pdf.GcPdfDocument.AcroForm), a default value is automatically assigned depending on the type of the current object's owner:
When setting this property, you may use GrapeCity.Documents.Text.FontCollection.FindFamilyName or other GrapeCity.Documents.Text.FontCollection methods to find a suitable font.