Listed Related Attachments is a WordPress plugin that will display a filtered list of all related attachments for the current post or page in the sidebar widget or in the content of the page via a shortcode.
The plugin can filter the list of attachments by mime/type such as image, image/png or application/pdf.
Detailed documentation, complete with examples of all the shortcode attributes, is available for general mind expansion.
The List Related Attachments source code is on GitHub for anyone to fork, modify and contribute improvements and bug fixes.
Free community support will always be available at the List Related Attachments WordPress Forum.