1. using finder select the PDF's to resize Holding Command key you can select multiple PDF's
Now right-click on the selected file > Open with > Adobe Acrobat
(Mac)
(windows)
2. Acrobat should open and have the PDF(s) opened in separate tabs.
Click the Optimize PDF in the right menu bar
3. Then Reduce File size > Single for one PDF OR Reduce Multiple files
4. Click Ok to continue, no need to change options here
5. Click Add Files > Add Open Files, select all and add files and then OK.
6. you have a few options here
1. where you want to save the resized files
2. keep the original files name OR to append to the file names,
3. to overwrite the original files or save a copy.
I recommend keeping the original save folder, appending "-resized" to the end of the file and uncheck "overwrite existing files (make a copy)
Acrobat will chug for a little bit and new compressed PDF's should show up in the original folder/file location