What lossless PDF compression can and cannot do: a measured test
By PDFEditor.ae · Published
Why we ran this test
Compression tools often promise large reductions without saying what kind of file they tested. We wanted numbers for our own lossless compressor that anyone could reproduce, including the cases where it does nothing.
Method
- Test files were created by us on 10 October 2026; no customer files were used.
- Text report: a 24-page HTML page of paragraphs and simple tables, printed to PDF by Google Chrome.
- Photo pack: four 2000×1500 JPEG images (about 1.1 MB each) on four pages, printed to PDF by Google Chrome.
- Two more files were produced by our own tools: the four photos converted with JPG to PDF, and the report merged with the photo pack using Merge PDF.
- Each file was run once through Compress PDF; sizes are the exact byte counts reported.
Results
A side result: merging the two Chrome files (4,896,473 bytes together) produced a 4,707,638-byte file, because Merge PDF already saves in the compact format.
- Text report: 265,818 → 107,784 bytes (59% smaller).
- Photo pack: 4,630,655 → 4,629,093 bytes (0%).
- Photos via our JPG to PDF: 4,627,792 bytes before and after (0%).
- Report + photos via our Merge PDF: 4,707,638 bytes before and after (0%).
What this means
Lossless compression helps text-heavy PDFs made by programs that store files loosely. It cannot reduce photos or scans, because it does not lower image quality. If your file is mostly images, resize the images instead.
Your results will differ: the reduction depends entirely on how the original file was made. The tool always shows the before and after size, so you can see what it did for your file.