Step 1: Click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "MakePdf" and then click OK
Step 2: Right click on your project select Manage NuGet Packages -> Search itextsharp -> Install
iText is a PDF library that allows you to CREATE, ADAPT, INSPECT and MAINTAIN documents in the Portable Document Format (PDF), allowing you to add PDF functionality to your software projects with ease. We even have documentation to help you get coding.
Step 3: Design your form as below

Step 4: Add code to button click event handler as below
private void btnSave_Click(object sender, EventArgs e)
{
using (SaveFileDialog sfd = new SaveFileDialog() { Filter = "PDF file|*.pdf", ValidateNames = true })
{
if (sfd.ShowDialog() == DialogResult.OK)
{
iTextSharp.text.Document doc = new iTextSharp.text.Document(PageSize.A4.Rotate());
try
{
//Save pdf file
PdfWriter.GetInstance(doc, new FileStream(sfd.FileName, FileMode.Create));
doc.Open();
doc.Add(new iTextSharp.text.Paragraph(richTextBox.Text));
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
finally
{
doc.Close();
}
}
}
}
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