Use an online PDF compressor (upload, compress, download)
Open the PDF in Adobe Acrobat, then use Save As Other → Reduced Size PDF
In Adobe Acrobat, use File → Save As → Optimized PDF, then reduce image quality and resolution
Reduce image resolution to 150–300 DPI in the PDF optimization settings
Downsample images to a lower resolution (especially for scanned PDFs)
Convert color images to grayscale (if acceptable) to reduce file size
Remove embedded fonts (if the tool provides this option) and re-embed only necessary fonts
Remove unused objects and metadata (use “Remove hidden information” / “Sanitize” options)
Flatten transparency (if applicable) to reduce complexity
Reduce or remove bookmarks, comments, and attachments
Delete unnecessary pages, then re-export the PDF
Recreate the PDF from the source (print to PDF) using “smallest file size” or low-quality settings
Use “Print to PDF” with a low/medium quality setting (Windows: Microsoft Print to PDF; macOS: Save as PDF with reduced quality)
For scanned documents, run OCR and then save as a “text + image” PDF with optimized settings
Use a PDF optimizer tool (e.g., Ghostscript-based workflows) to downsample and remove metadata
Use qpdf/gs to linearize or optimize structure when supported by your workflow
If the PDF was generated from images, resave source images at lower resolution before exporting to PDF
Batch-compress multiple PDFs using a desktop or command-line compressor
If the PDF contains large vector graphics, simplify or re-export those elements at lower complexity
Export from the original application with “low” or “minimum size” PDF preset (when available)