Set the target first
A 1MB target is realistic for many short documents. A 200KB target is much stricter and may only work for simple or low-page-count PDFs.
Guide
How to compress PDF size.
Watch image quality
Large photos and scans create large PDFs. Lowering image resolution and JPEG quality usually saves the most space.
Check the output
Always open the compressed result before uploading it. The goal is not only a smaller file; it still needs to be readable.