In addition to Related Sublists (aka linked lists) Sintel Forms also supports the use of Related Libraries (Document or Picture Libraries).
Using a related Document or Picture Library is pretty easy.
First, you must add a new Document or Picture Library into the site. If you already have a library created you can use it.
Next you need to add a lookup column to the Document or Picture Library that refers to the list in which you are intending to use Sintel Forms.
It is highly recommended to select 'Enforce relationship behaviour - Cascade delete' for the created lookup column. Thanks to this when the item of a list with Document Library will be deleted, the documents will be deleted as well. Otherwise, the deletion of documents could be problematic given the specific folder structure.
Now that the Document or Picture Library is created and is linked to the main list via a lookup column, you simply need to launch the Sintel Forms Designer and add the library into a container within a section. We recommend that libraries are added into a section on their own i.e. a section that doesn't contain other fields.
The option to download files added to a Document or Picture Library is only available once you have saved the form with the files added i.e. files you added can't be downloaded until you have saved the form.
That's it, the library you inserted is now ready for use!
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.