How to Compress a PDF: What Changes and How to Check the Result

PDF compression is not a guaranteed “make smaller” switch. A PDF may already use compressed images and streams, in which case rewriting it can produce little change—or a larger file. When a renderer recompresses photographs, the file can shrink but details can be lost.

What the PDFPK compressor does

The current tool accepts one PDF up to the application limit of 20 MB. When Ghostscript is installed, the server rewrites the file using its ebook preset. That preset can reduce image quality. If Ghostscript is unavailable, PDFPK attempts to rebuild pages with FPDI; that fallback may not reduce size and cannot parse every PDF.

Steps: compress and verify your PDF

1. Keep an untouched copy of the original document.
2. Open the Compress PDF tool and select one PDF file.
3. Run the compressor and download the new PDF.
4. Compare the two file sizes. Open the result and inspect small text, charts, photographs, and any signature or form fields.
5. If the output is larger or looks worse, keep the original. Try changing image export settings in the software that created it instead.

When compression helps—and when it does not

Scanned documents and PDFs with high-resolution photographs often have the most image data to reduce. Text-only files and already-optimized exports may not shrink. If you only need to send a few pages, use Split PDF instead of recompressing the entire document.

PDFPK does not promise a particular percentage reduction or lossless output. Do not use a recompressed copy as the sole archival or signed version unless you have checked that the document remains fit for purpose.