Have you looked at ‘tooltip’ functions where if your ‘instructions’ are brief that could help as users ‘hover over’ the field
but also, there is the ‘show message’ you could use or add in pages to your form (not to another form) where you can show all this to the users and then a ‘return’ button that takes them back to the form page they were one.
as to URL. the format of the URL will be determined where you wish to store your pdf files on this other server. Your IT people should be able to help you with this and also they will be able to advise of the ‘permissions’ you will need to apply to the files so your users can access them