If you (a foreigner) are planning on marrying a Vietnamese citizen, there is one piece of information that must be considered first:
Because marriage requirements are determined by individual provinces and provincial cities, THE VIETNAMESE CITIZEN must FIRST obtain the official list of requirements from the provincial People's Committee.
You (the foreigner) will not be allowed to obtain this.
Only your fiancée/fiancé or one of that person's parents.
If you are marrying a Vietnamese woman, be prepared for her to resist doing this herself.
She may tell you to get the official information sheet, but that won't be possible.
This is the most important piece of information because it will direct you as to which documents are absolutely necessary in that province.
Most embassies & consulates make a list available, but those lists cover all possible documents required in Vietnam.
You are only responsible for the documents required by the province where you'll be married.
No one in the forum can give you that official information.
They can only share anecdotal information which is often incomplete or confusing and lacking the correct document name.
Good luck with the process.