Open the PDF in Preview
Click File
Click Export
Choose Quartz Filter
Select Reduce File Size
Save the file
Use Adobe Acrobat’s Compress PDF tool
Use an online PDF compressor
Print the PDF to PDF with a smaller file size
Reduce image resolution before creating the PDF
Remove unnecessary pages from the PDF
Delete unused annotations and comments
Flatten form fields and layers
Convert large images to JPEG before saving
Save the PDF as optimized or compressed from the source app
Use third-party PDF compression apps on Mac