Compress PDF guide
Why a PDF Will Not Compress Much and What You Can Do
A PDF can stay large after compression because its size depends on the material already stored inside it, not only on its page count.
On this page
Start by identifying what makes the file large
A scanned PDF is usually a collection of full-page images. A digitally created report may instead contain compact text, vector lines, fonts, and a few images. Those two files can have the same page count and respond very differently to compression.
If photographs or scans dominate the document, image resolution and JPEG quality are the main opportunities for reduction. If selectable text and vector graphics dominate it, the source may already be close to a practical minimum.
Why Recommended may produce little or no reduction
Recommended mode tries to preserve the PDF's structure. It can remove avoidable overhead and rewrite the document efficiently, but it does not deliberately turn every page into a picture. PDFKaka does not publish a result when that pass would be negligibly smaller or larger than the source.
Common reasons include:
- embedded images were already compressed;
- the file contains mostly text and vector graphics;
- fonts and reusable resources are already stored efficiently;
- the document is short and fixed structural overhead is a large share of its size;
- previous compression has already removed most easy savings.
What Strong and Maximum change
Strong and Maximum render each page and rebuild it from compressed page images. This can help scans and photo-heavy PDFs, but it changes the nature of the document. Selectable text, links, form fields, accessibility information, annotations, and signature validity may be lost.
Use a stronger mode only when the destination mainly needs readable page appearance. Keep the original when anyone may need search, copying, forms, accessibility, or signature verification.
Decide whether another change will help
Removing genuinely unnecessary pages can reduce size because their content is no longer present. Repeatedly compressing an already compressed result usually adds visual damage without creating a useful reduction. If the file remains above a portal limit after an acceptable stronger pass, the requirement may be unrealistic for that page count and level of detail.
Compare the output at the zoom level or print size that matters. Small text, identification details, diagrams, and signatures should remain legible before the smaller file is accepted.
FAQ
Why can a compressed PDF be larger than the original?
A rewrite adds its own document structure. When the source is already efficient, that overhead can outweigh small savings; Recommended mode therefore avoids publishing a negligibly smaller or larger result.
Why does a text-heavy PDF barely shrink?
Text and vector instructions are often compact already. Large reductions usually come from lowering the resolution or quality of image-heavy pages.
Does stronger compression remove searchable text?
Strong and Maximum rebuild pages as images. Searchable text and other interactive document features may no longer be available in the result.
Should a scanned PDF use a stronger mode?
A scan may shrink more with Strong or Maximum because its pages are already image-based. Check small print carefully and keep the original.