I found out that statistics of PDFs that are clicked are recorded per this other forum post, and tested and see it under 'Clicks' as 'WordPress.com Media'.
However, unlike posts and pages, it is not something that can be tracked over time. As in, I can't click on a little magnifying glass to tell me the stats aggregated since the beginning of time (in my blog's world, that is). Is this something that can be done? This is important because PDFs uploaded are generally things you want to be able to track over time, like a post or a page.
The blog I need help with is alexanderchow.wordpress.com.