c# - How to append the file extension .pdf to a String entered by the user? -

i coding program need save texts (from rich text box) pdf.

i use itextsharp , code:

document doc = new document(itextsharp.text.pagesize.letter, 10, 10, 42, 35); pdfwriter wri = pdfwriter.getinstance(doc, new filestream("titleofpdf.pdf", filemode.create));//textbox1(in form) assign here title of document doc.open(); //open document in order write inside. paragraph paragraph = new paragraph(richtextbox1.text); // adds above created text using different class object our pdf document doc.add(paragraph); doc.close(); 

i title of file flexible , assigned user (from text box).

if change line:

pdfwriter wri = pdfwriter.getinstance(doc, new filestream("titleofpdf.pdf", filemode.create)); 

to:

pdfwriter wri = pdfwriter.getinstance(doc, new filestream(textbox1.text, filemode.create)); 

then works fine, but file hasn't got extension .pdf.

how can make title of document flexible user can assign it, , extension .pdf?

thanks user mkl found answere. had put:

textbox1.text + ".pdf"