Until the middle of the 18th Century, paper was made in individual sheets in wire frame baskets. That’s good for us and I can show you why. If you hold a piece of paper up against a bright light, and you don’t need a fancy bit of kit like this light box, any strong light will do, if the light reveals a pattern of fine parallel lines, those are the marks left by the wires in the basket, that’s called laid paper.
By contrast, if your paper has a uniform composition, if it’s smooth like this, that’s wove paper. That’s a completely different process that wasn’t invented until 1750. So if your sheet of paper is uniform, it’s wove paper, it’s modern. If it has the pattern of parallel lines, it could be much older.
The other thing you can do is look at the ink. The question with ink is whether it’s consistently strong or fades during the course of writing. If the quality of the ink in your document changes, if it goes from being darker to more faint then it’s likely to be from the 18th Century or before, when people had to dip their pens in the ink far more often. During the 19th century, steel or metal nibs were introduced, which meant that the quality of the ink was much more consistent. If this is the case then your document was written in the 19th Century or later.