If you are looking to printout certificates for your students, I would recommend visiting these two websites. They are both free and allow you to download the certificate as a pdf file.
Select your certificate design, personalize it, and simply download it as a pdf. In the design phrase, you must select the design category, formal, fun or kids, then select your design, personalize the certificate, then finally download it as a pdf file. Here is my sample certificate. It is quick and easy!
First, select the template you would like to you use from this website. There are many templates to choose from. Then, download it as a pdf file. Once this is completed, you can edit the pdf file and personalize it. This website does offer free templates, however, the certificate will contain the watermark. For $.99, you can download the premium version without the watermark. Here is my sample certificate.