Depending on what program you used to create a PDF, the file size of your PDF file can be quite large. If you combine two or three PDF files together using preview, you can also end up with a bloated PDF file. The best way to reduce PDF file size is with Acrobat professional, which can do all sorts of magic on PDF files. But here is a free way to make a PDF file smaller. Firstly, open the PDF file in ColorSync utility. The ColorSync utility is found in the utility folder of the applications folder of your computer. If you don’t know how to find that, simply right click ( or option click if you have a one button mouse) on the PDF file, and select from the menu open with, ColorSync utility.
This will open your PDF file in colour sync utility. Go down to the bottom of the window to the drop-down menu on the left that says ‘Filters’ and select ‘reduce File Size’. then click the button in the bottom right of the window that says apply.
This will go through and re-compress the images in your PDF to make the file size smaller. Don’t forget to save the file after you’re finished, you may want to use ‘save as’ so that you still keep the original copy of your PDF file.
If you want to be able to change the quality of the file that is saved, check out this great article from macworld: