Generally, it's already tracking out of the box but here are some steps to ensure it is.
Go to Launch
Click on the Extensions Tab
Find the Adobe Analytics Extension
Scroll to the Link Tracking Dropdown
Ensure PDF is listed there, if it isn't, add it.
Go to Adobe Analytics
Look for "Download Link" and you should see the PDFs.
Beyond this, you can actually setup link listeners for a specific PDF. Such as abc.pdf. There are different ways such as creating custom code to listen or using a CSS selector likea[src*="abc.pdf?"], a[src*="abc.pdf#"], a[src$="abc.pdf"] (not been tested)