Marketo Link to PDF hosted on external server

Yes, you should be able to do that.  If you share some PDF links, we can take a look

This link for example does not work internally for employees and our recipents outside our network have also experienced this issue:

mkto-n0077.com/track?type=click&enid=bWFpbGluZ2lkPW1vb2R5c0JldGFjdXN0LTEyMzUzLTMxNzc4LTAtMTAwMTUtcHJvZC05ODc0Jm1lc3NhZ2VpZD0wJmRhdGFiYXNlaWQ9OTg3NCZzZXJpYWw9MTM0ODYyODYwNyZlbWFpbGlkPWFsZXNzaW8uYmFsZHVpbmlAbW9vZHlzLmNvbSZ1c2VyaWQ9MTMwNTE3NyZleHRyYT0mJiY=&&&http://www.economy.com/home/products/brochures/databases-Historical-Forecast.pdf?mkt_tok=3RkMMJWWfF9wsRonua%2FMce%2FhmjTEU5z16u8tXKaxhYkz2EFye%2BLIHETpodcMTcJiNLzYEhcSI4JkxgVAR%2B2ac4RZ6Q%3D%3D

Links to webpages on our domain appear to be okay externally, but links to PDFs never seem to work.

I was able to access the PDF by following the link on my Chrome browser on Windows 7.  I would work with the service provider to figure out if they had any service/network outages.  This does not seem to be a Marketo issue.

I've experienced this problem myself and it happens a lot on firefox on a mac you can't download the pdf, and some versions of safari on a mac as well.  Either you can't download the pdf or there are some functionalities on the PDF you can't do such as downloading the file to your desktop or print. 

It's been suggested to turn off the marketo link tracker as a fix. 

I never link directly to a PDF to avoid issues. I create a landing page to download the link to ensure that no extra code conflicts with the PDF file. Here's an example: go.spotlighttms.com/WhitePaperLetters_CorporateTicketConsumerCaseStudyDownload.html