How to compress a PDF without unnecessary quality loss

Why PDF file sizes vary

A PDF is a container that can hold text, fonts, vector graphics, photographs, scanned pages, forms, attachments and other objects. A hundred-page text report can be smaller than a two-page photographic brochure. Page count is therefore a poor measure of expected file size.

Scanned documents are often large because every page is stored as an image. Embedded photographs, duplicated assets and unnecessarily high image resolution are other common causes. Some files have already been optimised and offer little room for further reduction.

What browser compression changes

Paperuna’s browser compressor renders each page and creates an optimised image-based PDF. Lower image resolution and stronger JPEG compression reduce the output size, particularly for scans and photographs. If the generated version is not smaller, Paperuna returns the original rather than lowering quality without a size benefit.

Flattening pages can remove selectable text, links, form fields, layers, annotations and certificate-based signatures. Use a copy and choose another workflow when those features must remain interactive.

Choose an appropriate setting

Low compression prioritises visual quality and suits documents that will be printed or closely inspected. Medium compression is a sensible starting point for email and routine screen reading. High compression targets the smallest file and is more likely to soften small text or image detail.

• Use low compression for print and detailed diagrams.
• Use medium compression for ordinary sharing.
• Use high compression for upload limits or quick-reference copies.
• Compare fine text, signatures and barcodes before distributing the result.

Measure more than the percentage saved

A dramatic saving is not automatically a good result. Open the output at 100% zoom, inspect its smallest important text, and print a representative page if printing matters. Check that stamps, signatures, line drawings and QR codes remain usable.

If the document was already small, a modest reduction may be the correct outcome. Repeatedly recompressing an image-based PDF can accumulate visible artefacts without producing meaningful additional savings.

Alternatives when quality must be preserved

Remove unnecessary pages, delete embedded attachments using suitable software, export source images at an appropriate resolution, or recreate the PDF from its original document. If searchable text and links matter, prefer an optimiser that can recompress images while preserving other PDF objects rather than flattening every page.