Use a PDF compressor tool
Save the PDF as a reduced-size file
Lower image resolution before exporting
Compress embedded images
Remove unnecessary pages
Delete unused fonts
Remove embedded metadata
Flatten annotations and form fields
Convert images to JPEG instead of PNG when appropriate
Reduce color depth
Optimize the PDF in Adobe Acrobat
Re-export the file with smaller page size
Use grayscale instead of color
Split large PDFs into smaller files
Remove bookmarks, comments, and attachments
Use a lower-quality scan setting
Recreate the PDF from the source file with smaller settings