Publishing a document proves nothing about whether it was edited before publication. Publishing its hash does. A SHA-256 value is a fingerprint: identical files always produce identical hashes, and changing a single character produces a completely unrelated value.
How to check any document on this site
Download the file, run sha256sum filename.pdf on Linux or macOS, or certutil -hashfile filename.pdf SHA256 on Windows, and compare the result to the published manifest. If they match, the file you have is byte-for-byte the file that was published.
Why an archive should do this
Because the alternative is asking readers to take an interested party’s word for it. See the source-of-truth standard and the verification guide.