You can accomplish the first part using the Quick Page/Post Redirect Plugin. Just set the Request URL to /resume and the Destination URL to /wp-content/uploads/2021/07/Resume-v4.pdf
For the second part of your question, you can add a redirect rule to your .htaccess file:
Redirect /wp-content/uploads/2021/07/Resume-old.pdf /resume
The way you worded your question you actually would set up an infinite redirect, so I changed it here to “Resume-old.pdf”.