Yes, you can convert a Formitize Invoice to a Job in both the Web Portal and the App
In the Web Portal go to Accounts > Invoices > select the Edit pen for the invoice that you would like to convert to job > Convert to Job at the bottom of the invoice > enter job details > Save.
In the App go to Accounts > Invoices > select the invoice that you would like to convert to a job > Convert to Job at the bottom of the invoice > enter job details > Save.