spirepdf c# change font of a textfield

Question

i am trying to populate a PDF using field names in PDF which i am able to do, however i want to change the font how can i do this

 public void FillPdf(string pdfTemplatePath, string outputPdfPath, Dictionary<string, string> fieldData, string fontPath, float fontSize)
 {
     Logger logger = new Logger(logFilePath);

        
     PdfDocument document = new PdfDocument(pdfTemplatePath);
     PdfFormWidget loadedForm = document.Form as PdfFormWidget;
        
     PdfTrueTypeFont trueTypeFont = new PdfTrueTypeFont(fontPath, fontSize); //not sure what to do from here

     //Go through the forms
     for (int i = 0; i < loadedForm.FieldsWidget.List.Count; i++)
     {
         PdfField field = loadedForm.FieldsWidget.List[i] as PdfField;
         //Fill textbox form field
         if (field is PdfTextBoxFieldWidget)
         {
             PdfTextBoxFieldWidget textField = field as PdfTextBoxFieldWidget;
             //Get the field name and fill with content
            foreach(var f in fieldData)
             {

                 if (textField.Name == f.Key)
                 {
                     
                     textField.Text = f.Value;                               
                 }                         
             }
         }
        

     }


     loadedForm.FieldsWidget.FormWidget.ReadOnly = true;
     //Save and close
     document.SaveToFile(outputPdfPath,FileFormat.PDF);
     document.Close();

 }

when i try to do this PdfTrueTypeFont trueTypeFont = new PdfTrueTypeFont(fontPath, fontSize); and do

if (textField.Name == f.Key)
{
    textField.Font = trueTypeFont;
    textField.Text = f.Value;                               
}   

my program fails can someone help me figure a way out of this please.