The ID of the document is is the Visual-Meta ID which is created like this:

{2021-7-17T18:00:00:00Z/documentti} < start with date and time the document’s metadata/Visual-Meta was ‘created’ (in UTC), then the first 10 characters of the document title, or less.
(In the ACM pilot is is simply the DOI: vm-id = {doi10.1145/3372923.3404798})

OR like this, if the Visual-Meta was appended by reader software rather than added on creation:

{appended-hash-sha256-98765435678987654;reader(3.0)} < For documents which are already created (without Visual-Meta) where the reader software appends a vm-d for future reference. It is a hash of original PDF before Visual-Meta page is added, using a sha256 of the raw string value of the document, followed by the name and version of the software appending the vm-id.