Large size PDFs are always troublesome to send out or save, here I collect some tips to reduce PDF file size on mac:

# Small Tips (Without using PDF Compressor)
1) Make the images in the PDF file in small size, images are always the reason to keep a PDF file larger;
2) Delete and remove some unnecessary pages in the PDF file;
3) Export PDF to other formats, especially when you are working on a scanned PDF or a PDF mainly composed of images, you can convert to Text, Word or other editable formats;

# Using PDF Compressor
1) Dedicated---Cisdem PDF Compressor
2) Mac Preview(free)
3) smallpdf(online free)

Also, you can find the details here: https://www.cisdem.com/resource/shrink-pdf-file-size-on-mac.html