You can compress a PDF without losing image quality using the Acrobat online PDF compressor. The tool balances an optimised file size against the expected quality of images, fonts, and other file content. To compress a PDF, drag and drop it into the tool above and let Acrobat reduce the file size without compromising quality.
For more refined control of optimisation settings, you can try Adobe Acrobat Pro DC for free for seven days. Acrobat Pro DC for the Mac or Windows operating system lets you customise PPI settings for colour, grayscale and monochrome image quality. You can also use PDF editor tools, edit scans with OCR functionality, convert PDFs to Microsoft PowerPoint and other file formats, convert PNGs and other image file formats, organise and rotate PDF pages, split PDFs and more.