iTextsharp special characters not being filled into PDF form

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C#

WinForms

itextsharp

iTextSharp is not inserting special characters (serbian letters: P,Š,Đ,Č,Ć,Ž) into PDF Form. Can you please help me with editing my code to fix that issue. Thanks in advance.

What I have tried:

This is my code:

private void BtnSaglasnost_Click(object sender, EventArgs e)
        {
            IzlistajImenaPolja();
            PopuniFormu();
        }

        private void IzlistajImenaPolja()
        {
            string pdfTemplate = @"C:\UDDKT\PDF\Saglasnost.pdf";

            this.Text += " - " + pdfTemplate;

            PdfReader pdfReader = new PdfReader(pdfTemplate);
        }

        private void PopuniFormu()
        {
            string pdfTemplate = @"C:\UDDKT\PDF\Saglasnost.pdf";
            string newFile = @"C:\UDDKT\PDF\Saglasnost_Popunjena.pdf";
            PdfReader pdfReader = new PdfReader(pdfTemplate);
            PdfStamper pdfStamper = new PdfStamper(pdfReader,
                new FileStream(newFile, FileMode.Create));
            AcroFields pdfFormFields = pdfStamper.AcroFields;

            pdfFormFields.SetField("FrmIme", TxtIme.Text);
            pdfFormFields.SetField("FrmPrezime", TxtPrezime.Text);
            pdfFormFields.SetField("FrmBrojLK", TxtBrojLK.Text);
            pdfFormFields.SetField("FrmDatum", TxtDatumAkcije.Text);

            pdfStamper.FormFlattening = false;

            pdfStamper.Close();
        }