How to compare two pdf files and find the difference in terms of percentage

my code like as

private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.CheckFileExists = true;
            openFileDialog.AddExtension = true;
            openFileDialog.Filter = "PDF files (*.pdf)|*.pdf";
            DialogResult result = openFileDialog.ShowDialog();
            if (result == DialogResult.OK)
            {
                filename = Path.GetFileName(openFileDialog.FileName);
                path = Path.GetDirectoryName(openFileDialog.FileName);
                textBox1.Text = path + "\\" + filename;
            }
        }
 
        private void button2_Click(object sender, EventArgs e)
        {
 
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.CheckFileExists = true;
            openFileDialog.AddExtension = true;
            openFileDialog.Filter = "PDF files (*.pdf)|*.pdf";
            DialogResult result = openFileDialog.ShowDialog();
            if (result == DialogResult.OK)
            {
                filename = Path.GetFileName(openFileDialog.FileName);
                path = Path.GetDirectoryName(openFileDialog.FileName);
                textBox2.Text = path + "\\" + filename;
            }
        }

compare two pdf files and find the difference in terms of percentage

please help me.thank u