There is the option to allow users to register themselves in order to join the community. This would allow them enter the pre-determined required fields and in turn allow them to view attachments or view documents as a pdf. However Jive does not have a pop-up modal that would allow for quick contact details before proceeding with the site. If this is something you would like to see in future releases I would recommend creating an feature request for it here Ideas for Jive. This will allow others to vote up the idea and help it gain visibility.