Thanks Jason. I was able to get Slimstat to track it by adding “php” as an extension to track as downloads (these are the only links that use the file extension, so it’s fine). The links are managed outside of WordPress, which likely explains why it wasn’t working with Slimstat out of the box (though I had tried adding the tracking code in Settings to no avail). All’s well that ends well — Slimstat is working great now. Thanks for all your help!
That is already enabled, but the link spawns PDFs using a slug like this: https://domain.com/viewer/index.php?id=1032
Slimstat isn’t tracking the clicking of that link as an outbound link or a download.