Compress the PDF using an online compressor tool
Save/export the PDF with “Reduce file size” or similar compression settings
Lower image resolution (e.g., 300 dpi to 150–200 dpi) during export
Convert images to a more efficient format (JPEG for photos, remove embedded unnecessary PNGs)
Downsample embedded images inside the PDF
Reduce image quality/bit depth in the export settings
Remove unused embedded objects and resources (fonts, metadata, thumbnails)
Flatten layers and remove transparency where possible
Convert vector elements to images only when it reduces size
Remove duplicate fonts and subset fonts when exporting
Disable “embed all fonts” if embedding is not required
Remove bookmarks, thumbnails, and annotations if not needed
Remove or reduce metadata (document info, XMP)
Recreate the PDF using a “printer”/export option that supports optimization
Use PDF/A settings carefully (they can increase size depending on content)
If available, use “Optimize PDF” / “PDF Optimizer” features in your software
Split the PDF into smaller sections if the goal is easier sharing
Use tools that support “linearized”/web-optimized PDFs when appropriate