only you need to add this content on your page
Response.ContentType = "application/pdf";
Response.AddHeader("content-disposition", "attachment; filename= SampleExport.pdf");
Even you can format the text also,if you want to set the page with A4 or any other even you can also do the same.you can also specify the font size, style color all the basic things you can do with it.
you can download the code from the below link. you can try that it will helps you.