Start terminal and navigate to the folder containing the PDF file.
Type the Ghostscript command to reduce the size of PDF file. For example, if file is named “file1.pdf” and you want the reduced version to be called “file2.pdf,” type the following command at the terminal prompt:
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=file2.pdf file1.pdf
Press the “Enter” key to execute Ghostscript command.