How can i make my PDF a fillable one without creation from a blank.

Unfortunately, there is no way to turn a PDF into a fillable one. You can only turn you web form as a fillable PDF form, and also import your own existing fillable PDF form: 

https://www.jotform.com/help/552-How-to-Create-PDF-Forms-with-PDF-Editor

https://www.jotform.com/help/548-How-Can-I-Import-My-Own-PDF-to-JotForm

Let us know if you have more questions, we will be glad to assist you.