It doesn’t work because you don’t have any DNS records created for that subdomain www, traffic needs to flow to Cloudflare to hit a rule. You could create a Proxied AAAA record with a value of 100:: (IPv6 Discard), which Cloudflare recommends to use for sites without origins/that will just be using Cloudflare features.
However, in this case, the public r2.dev links are not meant for production as they are rate limited. Instead, I would add your domain as a Custom Domain for the R2 bucket: Public buckets · Cloudflare R2 docs, and then you could simply name your file resume.pdf and access it that way, same for any other file.
If you’re trying to describe the behavior of showing content from another page/URL on your own website/without changing the URL, that’s not a feature Cloudflare offers, and that’s not what Page Rules do, they would simply redirect the visitor to that URL, which their address bar would reflect.