Pop-up blockers are generally used to prevent unwanted content (ads and the like) appearing on your web browser.  Unfortunately they also stop PDF documents as well.  See below for instructions for popular web browsers:

Allowing pop-ups in Chrome

Allowing pop-ups in Firefox

Allowing pop-ups in Microsoft Edge

Allowing pop-ups in Safari

If you experience any problems accessing any of the Library's E-Resources, please let us know - you can email the details to library@st-andrews.ac.uk