Yes, redirects w/PDFs are a special non-working case AFAIK.
Aside from switching to serving all your Marketo assets via CDN (where all asset types can be redirected equally) I'm not aware of a solution. A primitive approach is to create a single-page PDF with a button/link to the new page.
Note that if you're worried about old links in emails, you can run your own tracking server as well -- in which case you'd get first dibs on redirecting people from click.example.com branding domain before they hit your pages.example.com LP domain. But this is not for the faint of tech skills and it's unlikely most people would want to do this (I like the control it gives you, but even I don't tell my clients to do it unless they ask).