Can we upload external forms and use them through this site?

Also, if we have forms that we created outside of JotForm, can we upload and use them through this site?

Yes, if you have fillable PDF forms, you can use our Fillable PDF Form creator to import your forms.

Please check this related guide: https://www.jotform.com/help/548-How-Can-I-Import-My-Own-PDF-to-JotForm 

Do review and let us know if this suits your requirement.