Can I prefill the form?

Yes, you can prefill your form. 

You can use our prepopulate app to prepopulate your form: http://prepopulate.jotform.io/ 

You can also prepopulating fields via URL parameters. Inside of this guide you can find how to do it:

http://www.jotform.com/help/71-Prepopulating-fields-to-your-JotForm-via-URL-parameters 

Hope this will help. Let us know if you need further assistance.