mac – Reduces the size of the pdf text file scanned with the application

I had scanned 11 sites of a black and white document and exported it in pdf format. With two different known applications, I got a file size of about 8 MB. I've tried different solutions with the ColorSync filter or the ghostScript commands, but the size of the PDF file is getting smaller not.

With the scans of a printer, I got pdf files with about 10% of that size without loss of quality. Does anyone know how to reduce a large pdf file?