custom file type filter on form page

[PedroBuffon]

Right now the only way to allow only a specific file type to be uploaded is to globally block all other file types, but if you want to block let's say PDF for one form and allow other file type on another form, you can't. My use case is we use excel for gym class information of teachers, sometimes they send it in PDF but we have to refuse. so blocking all but excel files on one form is useful.