How do I track PDF downloads?

You can detect interactions with a PDF file on your site via click tagging.

There are four types:

• Exit

• Download

• Action

• Navigation

The click's type is set during the implementation.

The Piano Analytics Developers documentation will give you the information you need to set this up: https://developers.atinternet-solutions.com/piano-analytics/data-collection/how-to-send-events/standard-events#clicks

Please note that once the tag has been implemented, you can use Piano Analytics' Tag Inspector plugin for Chrome.
You will thus be able to directly review your tagging (this goes for tagging in general not just clicks).

It is up to you to decide on the click type you wish to push based on existing tags and the way you want your data to be displayed in the interface.