Why is my PDF still large after compression?

A PDF can contain very different kinds of data

A short text document can already be small. A scanned PDF often stores each page as an image, so resolution and image encoding account for much of its size. Two PDFs with the same page count can therefore have very different compression potential.

Our synthetic scan below is a full-page image without text recognition. It is useful for measuring image compression, but it is not a representative scan of every real document.

Use the preset that matches the document

Light optimizes structure. Balanced and Strong additionally optimize supported embedded images. Start with Balanced, inspect the smallest text and fine lines in the preview, and try Strong only if the result remains readable.

Compression retains existing text but does not add OCR. Text inside a scanned picture does not become selectable simply because its PDF has been compressed.

Know when to keep the original

Previously optimized files may have little room left. Some complex image structures are preserved rather than rewritten. When a valid smaller result cannot be produced, FormatOwl returns the original with a notice; repeated compression is not a way to guarantee further savings.

Encrypted and digitally signed PDFs are rejected. Review forms, important pages and colors before distributing the result. FormatOwl does not recertify PDF/A or guarantee every special interactive feature.

Two one-page PDFs, same Strong preset

Measured locally on September 16, 2026 with generated content. The text sample saved only 431 bytes; the scan offered much more room. This is not a guarantee for your document and does not measure OCR or archival compliance.

Related tools

• PDF compressor
• Image compressor