Ideas for simple line Item Invoices (using 3rd party)

Hi everyone, I want to make a feature in app that allows employees/contractors send their biweekly invoices for their hours/services. Ideally it would have several lines in case they do something other than the standard. I will add a picture below of what I want and almost accomplished through Pandadoc.

My problem with this ^ is that the user (employee) is not able to edit the services provided nor the rate fields. They would have to be prefilled by me which defeats the purpose.

Does anyone know of an integration I can use to accomplish this? It would have to have dynamic entry fields to minimize the back end work on Glide, because generating back end line items can get nasty and eat massive row quantities

Edit: to avoid confusion, the app would just take a few token fields and send a document from a template for them to fill out externally (and hopefully with a signature field).