How to delete tiny pixel and trim only printed area in scan document?

[Jonastrong]

First, I want to trim the printed part as a rectangle and see it. But the scan is not constant, so it is not easy to crop so many documents by hand. And it was scanned with a machine, very small, 1~2 radius size black pixels are hidden. The attached photo is enlarged so that such pixels can be easily viewed by adding a Stroke Style to the Layer Mask.

It's easy to erase it one by one because it's visible. However, the Trim command doesn't have tolerance, the color of the erased part and the original background color are very finely different so it doesn't work.

How can I cut the printed parts into rectangles?

[Jonastrong]

I mean how to crop only printed area of scanned document.