There are languages used today that don't have a separate word for "the", such as Hebrew (which uses a prefix to denote "the"), or Chinese, which apparently doesn't use articles.[1]

Also, knowing what the most common words are wouldn't really help you much if you didn't know what the documents are about. For example, if they were trade records, they might contain a lot of text saying something like "X agrees to buy 20 pounds of olives from Y for $50 if delivered by next week". But if they were historical records of wars, other words may be more common.

[1] https://mylanguages.org/chinese_articles.php