Hi I was wondering about this too! It looks like you can get the permalink from the uploaded file in GitHub, paste it into your browser and switch the 'https://github.com" to "https://raw.githubuser.content.com" and remove the blob

https://github.com/NatalieRMCastro/nataliermcastro.github.io/blob/07d90332dd0a4d94d3f893734734061c72f7b9bc/assets/images/Decision%20Tree%20-%20News%20Headlines%20Partisan%20Affiliation%20Entropy.pdf

⬇️

https://raw.githubusercontent.com/NatalieRMCastro/nataliermcastro.github.io/07d90332dd0a4d94d3f893734734061c72f7b9bc/assets/images/Decision%20Tree%20-%20News%20Headlines%20Partisan%20Affiliation%20Entropy.pdf

to get an embed url for the iframe viewer:

<iframe
  src="https://mozilla.github.io/pdf.js/web/viewer.html?file=THE ABOVE LINK HERE"
  width="100%"
  height="600px"
  style="border: none;">
</iframe>