Using C# PDF SDK
C# PDF Builder: How to draw, add a rectangle shape to PDF file

...
PDFContext ctx = new PDFContext();
//  set figure size: width 600 pixels; height 100 pixels
ctx.SetWidth(new RELength(600, Units.PX));
ctx.SetHeight(new RELength(100, Units.PX));
//  draw 2 rectangles
ctx.DrawRectangle(new REPen(new REColor(0, 255, 0)), 250, 10, 100, 80);
ctx.DrawRectangle(new REPen(new REColor(0, 255, 255), 3F), 200, 20, 300, 60);
Figure figure = new Figure(ctx);
document.Add(figure);
...

String outputFilePath = Program.RootPath + "\\" + "Sample25.pdf";

Document document = new Document();
PDFBuildHandler.Create(document, outputFilePath);
//  open document
document.Open();
//  create Figure
PDFContext ctx = new PDFContext();
...
...
Figure figure = new Figure(ctx);
document.Add(figure);
//  close document and save to the output file
document.Close();