In the PDF viewer only the http:// URLs are recognized and clickable, not the logseq:// ones.
Other PDF viewers like Okular let me click logseq:// links, ironically Logseq’s built-in PDF viewer doesn’t support its own URI scheme.
It would be very useful to have this because one can create its own PDFs of notes or even mindmaps and illustration that can be viewed everywhere with links to open Logseq notes when installed.
Of course being able to do so without an external PDF viewer is better.