Option1: Mess around with Document optimizer in PDFStudio.
Option2: See following command (sometimes works better than PDFStudio, esp. for images)
Use the following ghostscript command:
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
-dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
Summary of -dPDFSETTINGS:
-dPDFSETTINGS=/screen lower quality, smaller size. (72 dpi) -dPDFSETTINGS=/ebook for better quality, but slightly larger pdfs. (150 dpi) -dPDFSETTINGS=/prepress output similar to Acrobat Distiller “Prepress Optimized” setting (300 dpi) -dPDFSETTINGS=/printer selects output similar to the Acrobat Distiller “Print Optimized” setting (300 dpi) -dPDFSETTINGS=/default selects output intended to be useful across a wide variety of uses, possibly at the expense of a larger output file
Reference: https://www.ghostscript.com/doc/current/VectorDevices.htm#PSPDF_IN:
Controls and features specific to PostScript and PDF input
-dPDFSETTINGS=configuration
Presets the “distiller parameters” to one of four predefined settings:
/screen selects low-resolution output similar to the Acrobat Distiller (up to version X) “Screen Optimized” setting. /ebook selects medium-resolution output similar to the Acrobat Distiller (up to version X) “eBook” setting. /printer selects output similar to the Acrobat Distiller “Print Optimized” (up to version X) setting. /prepress selects output similar to Acrobat Distiller “Prepress Optimized” (up to version X) setting. /default selects output intended to be useful across a wide variety of uses, possibly at the expense of a larger output file.
The exact settings for each of these, including their DPI values, are shown in the dozens of options in this table: https://www.ghostscript.com/doc/current/VectorDevices.htm#distillerparams.