Large PDF files are difficult to email, upload and open on mobile connections. The best compression result is not simply the smallest possible file; it is the smallest file that still looks professional and remains easy to read.
Start with the original document
If you still have the Word, PowerPoint or design source, remove unused pages, crop oversized images and export a fresh PDF. Repeatedly compressing an already compressed PDF can introduce fuzzy text and visible blocks around photographs.
Choose the right compression level
Use a balanced setting for documents that contain both text and photographs. Strong compression is useful for quick previews, but official forms, invoices and portfolios should keep enough resolution for small print and fine lines.
Check the important pages
After processing, zoom in on signatures, QR codes, diagrams and small text. Also check the first and last page, because cover artwork and footer text often reveal quality problems first.
Reduce image weight intelligently
Photographs usually create most of a PDF file size. Resizing very large photos before creating the PDF produces better results than aggressively compressing the final document. For screen reading, images rarely need print-level dimensions.
Keep a safe original
Download the compressed result with a new filename and keep the original until the new version has been reviewed. This simple habit makes it easy to try another compression level without losing quality.