iText7 TextRenderInfo.GetFontSize() usually produces a false result

Question

I am trying to extract the text and would like to store the correct font and font sizes for each text that is output. I have four test pdf's with which I am testing, three return the value 1 and one has the correct font size. What could be causing the problem, what are the solutions?

Here is my code:

using System.Text;
using iText.Kernel.Pdf;
using iText.Kernel.Pdf.Canvas.Parser;
using iText.Kernel.Pdf.Canvas.Parser.Data;
using iText.Kernel.Pdf.Canvas.Parser.Listener;

namespace PDFTextExtraction
{
    class Program
    {
        static void Main(string[] args)
        {
            string pdfFilePath = "pathtopdf.pdf";

            using (PdfReader pdfReader = new PdfReader(pdfFilePath))
            {
                using (PdfDocument pdfDocument = new PdfDocument(pdfReader))
                {
                    MyTextEventListener listener = new MyTextEventListener();

                    for (int pageNum = 1; pageNum <= pdfDocument.GetNumberOfPages(); pageNum++)
                    {
                        PdfPage page = pdfDocument.GetPage(pageNum);
                        PdfCanvasProcessor parser = new PdfCanvasProcessor(listener);
                        parser.ProcessPageContent(page);
                    }

                    Console.WriteLine("Extrahierter Text mit Schriftart und Schriftgröße:");
                    Console.WriteLine(listener.GetExtractedText());
                }
            }
        }
    }

    public class MyTextEventListener : IEventListener
    {`your text`
        private readonly StringBuilder extractedText = new StringBuilder();

        public void EventOccurred(IEventData data, EventType type)
        {
            if (type.Equals(EventType.RENDER_TEXT))
            {
                TextRenderInfo renderInfo = (TextRenderInfo)data;
                string text = renderInfo.GetText();
                string font = renderInfo.GetFont().GetFontProgram().ToString();
                float fontSize = renderInfo.GetFontSize();

                extractedText.AppendLine($"Text: {text} | Schriftart: {font} | Schriftgröße: {fontSize}");
            }
        }

        public ICollection<EventType> GetSupportedEvents()
        {
            return new List<EventType> { EventType.RENDER_TEXT };
        }

        public string GetExtractedText()
        {
            return extractedText.ToString();
        }
    }
}

I have already tried the following:

float ascent = renderInfo.GetAscentLine().GetStartPoint().Get(1);
float descent = renderInfo.GetDescentLine().GetStartPoint().Get(1);
float fontSize = ascent - descent;

I had a version with iTextSharp 5.5.13 and it worked flawlessly?

I did some research and found out that the Pdf operators are defined as follows:

BT 
0 0.6 0.95 0 k 
/GS0 gs 
/T1_0 1 Tf 
0.024 Tc 
-0.024 Tw 
8 0 0 8 32.3386 171.361 Tm
[(V)43.2(o)2.2(r)-1(n)1.5(ame)24( Na)7.9(c)-1.4(h)-1.1(n)1.4(a)0.5(me)] TJ
ET

The font size is defined here as 1? So the font is also defined? I am not a Pdf specialist, but maybe someone here can help me? The correct font size is 8pt.

if I do the following does it work?

 Matrix textMatrix = renderInfo.GetTextMatrix();
  float scaleX = textMatrix.Get(Matrix.I11);
  float scaleY = textMatrix.Get(Matrix.I22);
  float _fontSize = (scaleX + scaleY) / 2;