Adobe has a tool that lets you compress PDFs for free online. But you will have to save the file to the Adobe Document Cloud and agree to terms of use, etc.
https://www.adobe.com/acrobat/online/compress-pdf.html
With Adobe Pro, the Optimize feature might work, but that costs a lot of money. I think even the free version of Adobe Acrobat DC doesn't have free compression.
Gizmo's Best suggests some free PDF tools, including software that does compression:
https://www.techsupportalert.com/bes...ght=compressor