Linked Lists-How to add attachments
Attachments can be added to a form by using the attachments option from the top menu bar but it’s also possible to add them directly into a linked list or library directly on the form. To do so you simply need to make the ‘Attachments’ column visible (in the Designer Layout section, properties of the Linked List) and once this is set you will be able to add attachments within linked list on the forms.
When using linked lists or libraries standard SharePoint permissions apply i.e. you must ensure your users have contribute permissions on any linked list or library to ensure they can add items into those linked lists from the main form.