Microsoft Office Spoofing Vulnerability

According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do?
Exploitation of the vulnerability requires that a user open a specially crafted file.
In an email attack scenario, an attacker could exploit the vulnerability by sending the specially crafted file to the user and convincing the user to open the file., In a web-based attack scenario, an attacker could host a website (or leverage a compromised website that accepts or hosts user-provided content) containing a specially crafted file designed to exploit the vulnerability.
An attacker would have no way to force users to visit the website. Instead, an attacker would have to convince users to click a link, typically by way of an enticement in an email or instant message, and then convince them to open the specially crafted file.

According to the CVSS metric, the attack vector is local (AV:L) but no privileges are required (PR:N) and user interaction is required (UI:R). How could an attacker exploit this spoofing vulnerability?
The attack itself is carried out locally by a user with authentication to the targeted system. An attacker could exploit the vulnerability by convincing a victim, through social engineering, to download and open a specially crafted file from a website which could lead to a local attack on the victim computer.

According to the CVSS metric, successful exploitation of this vulnerability could lead to total loss of integrity (I:H)? What does that mean for this vulnerability?
The vulnerability could allow an unauthenticated attacker to insert malicious content into a document which then passes the authentication check when a partial signature is present.

Security updates
https — https://docs.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates
16.0.5413.1000 — https://support.microsoft.com/help/5002457
16.0.5413.1000 — https://support.microsoft.com/help/5002498
16.0.5413.1000 — https://support.microsoft.com/help/5002100
15.0.5589.1000 — https://support.microsoft.com/help/5002477