External links are needed when making a card link to a PDF open in a new tab or another external link open in a new tab.
Go to Add Content --> Misc. ---> External link
Fill out the needed details
Then Save. External links do not require publishing.
How to find the URL of a PDF
View the PDF in Cascade, under the file name, you'll find the path. Simply add https://www.csuchico.edu/ to the path and that will be the URL to the PDF
In this example, the URL is https://www.csuchico.edu/eop/_assets/documents/16-17eospar-eop-a.pdf
Adding an External link to a Card
Under the link settings for the card, select External, then click on Choose Link to browse for the created external link.
Select the created external link.
Once selected.
Save changes.