XHtmlOptions FontSubstitute Property. Whether font substitution should be used to reduce file size. ABCpdf .NET PDF Library. From ABCpdf .net previous page next page FontSubstitute Property Type Default Value Read Only Description [C#] bool [Visual Basic] Boolean true No Whether font substitution should be used to reduce file size. Notes This property determines whether font substitution is enabled. In many situations default built-in fonts can be substituted in place of the specified fonts. This can result in a substantial increase in speed and a considerable reduction in file size with little or no loss in output quality. Example None. previous page start next page