First of all you need to download "iTextSharp" from: iTextSharp
After that,extract iTextSharp and you need to add reference to file itextsharp.dll Chose right click on project-->add reference-->browse and browse to the extracted folder.
Now,you need to create pdf file on c:\ drive using this code:
Using fs As New IO.FileStream("c:\file.pdf", IO.FileMode.Create)
Using doc As New Document
Dim pdfWriter As pdf.PdfWriter = iTextSharp.text.pdf.PdfWriter.GetInstance(doc, fs)
doc.Add(New Paragraph("Now pdf file is created and you can input what you need!"))