We benchmarked the most popular PDF compression services on three real-world test files: a 12 MB scanned legal contract (mixed text + images), a 4.2 MB designer portfolio (high-resolution images), and a 28 MB academic thesis (200+ pages of mostly text). All tools were configured to their default "balanced" or "recommended" compression level. Results updated May 2026.
Each file was uploaded (or loaded locally for browser-based tools) to PDFKits, PDF24, iLovePDF, Smallpdf, Adobe Acrobat (Pro DC), and Sejda. We measured three metrics: output file size, visual fidelity (loss vs. original at 100% zoom), and end-to-end time from upload click to download complete. Tests were run on Chrome 126 over a 100 Mbps connection, with the same input file each time. We re-ran each test three times and used the median.
On the 12 MB scanned contract, PDFKits Compress PDF produced a 2.1 MB output (82% reduction) at 3.4 s total time, with no visible quality loss at 100% zoom. PDF24 achieved similar reduction (2.3 MB) but took 14 s due to server round-trip. Smallpdf and iLovePDF were comparable on size but both upload your file to remote servers. Adobe Acrobat's "Reduce File Size" preset produced 3.1 MB — larger output, but with explicit DPI control.
Browser-based compression (PDFKits, PDF24's local mode) avoids the network round-trip entirely: your 12 MB file doesn't have to leave your device and come back. On a typical home connection (50-100 Mbps up), upload alone takes 2-5 seconds for files above 10 MB. Browser-based tools start processing immediately. Beyond speed, the privacy advantage is structural: your PDF never reaches a third-party server, which matters for legal contracts, medical records, and confidential business documents.
For target-size compression (fit in an email, fit a portal upload limit), see our dedicated tools: 100 KB, 200 KB, 500 KB, 1 MB. For email-specific tips, see our Compress PDF for Email guide.