Compress PDF Online
Reduce File Size Instantly

PDF compression means reducing the number of bytes needed to store a document. There is no single switch that makes every PDF dramatically smaller without consequences. A scanned 100-page document may shrink considerably when its high-resolution page images are downsampled. A small text-only PDF may already be efficient and show almost no improvement. A professionally optimised file can even become larger when it is rebuilt with unsuitable settings.

This page provides two honest approaches. Lossless cleanup loads the PDF and saves its pages into a fresh container. It avoids deliberate visual degradation, but the result may only be slightly smaller—or not smaller at all. Image-based compression renders each selected page, saves it as JPEG and places that image into a new PDF page. This method can reduce image-heavy files more aggressively, but it flattens searchable text, hyperlinks, annotations, form fields, layers and vectors into page pictures.

Why results differ from one document to another

File size depends on page count, image resolution, colour depth, image format, embedded font subsets, duplicated objects, transparency, attachments and previous optimisation. Two PDFs with the same number of pages can have completely different sizes. That is why a trustworthy compressor should report the actual result rather than claiming that every file will be reduced by a fixed percentage.

Compression is not the same as ZIP

Putting a PDF in a ZIP archive may produce little benefit because many PDF streams and images are already compressed internally. PDF optimisation works inside the document by rewriting objects, reducing image data or removing unnecessary information. Image-based compression goes further by creating a simplified visual copy of every selected page.

Start with the lowest-risk method

When the PDF contains selectable text, digital signatures, interactive forms, bookmarks, accessibility tags or important vector diagrams, try lossless cleanup first. Even if the saving is small, it avoids deliberately turning the document into page images. For a scanned PDF or a file made mainly from photographs, recommended image compression is often a more useful starting point.

Use DPI to control page detail

DPI determines how many rendered pixels are created from each PDF page. Higher values make small text and thin lines clearer, but increase memory use and output size. Around 96 to 120 DPI is often suitable for normal screen viewing. Around 150 DPI may help with detailed reports. Higher values are not automatically better when the goal is a small upload copy.

Use JPEG quality to control compression artifacts

JPEG quality affects how aggressively the rendered page image is compressed. Low settings can create blockiness, ringing around letters and blurred gradients. High settings preserve detail but reduce fewer bytes. The recommended 72% setting is designed as a practical midpoint, not as a universal best setting.

Check the smallest and most important content

After downloading, zoom into small print, signatures, stamps, QR codes, barcodes, diagrams, tables and screenshots. A document that looks acceptable at fit-to-page view may still have damaged detail. Never delete the original until the compressed copy has been opened and checked page by page.

Compressing scanned PDFs

Scanned documents are usually collections of page images. Their size is influenced by scan resolution, colour mode and image compression. A scan captured at a very high resolution may contain more detail than normal screen reading needs. Rendering at a lower DPI and encoding as JPEG can therefore reduce the file substantially. Grayscale may reduce it further when colour is unnecessary.

Compressing text-based PDFs

A digitally generated PDF may contain compact text commands and embedded font subsets. Turning those pages into JPEG images removes selectable text and can produce a larger result. Lossless cleanup is safer for these files, although the size reduction may be modest. Where possible, optimise the source document or export it again using suitable PDF settings.

OCR and searchable text

Optical character recognition adds a searchable text layer to scanned documents. Image-based compression on this page creates page images and does not rebuild an OCR layer, so the output may no longer support text selection or searching. Keep the original OCR PDF when accessibility or document search is important.

Forms, links, comments and signatures

Interactive PDF elements are not ordinary page pixels. Raster compression flattens their visible appearance, but does not preserve the original interactive behaviour. Digital signatures can become invalid when a signed document is changed. Use lossless cleanup cautiously and avoid modifying signed legal or official records unless your workflow explicitly permits it.

Colour documents versus grayscale

Grayscale can lower image data for black text, monochrome forms and many scanned records. It is inappropriate when colour carries meaning, such as highlighted revisions, medical imagery, maps, branding, charts or coloured signatures. Review the document's purpose before removing colour.

Archival and print documents

A highly compressed screen copy should not automatically replace a high-resolution print file or archival PDF. Professional printing may require specific colour profiles, embedded fonts, bleed, transparency handling and PDF standards. Archival documents may require formats such as PDF/A and reliable text preservation. Keep a trusted master and create a separate lightweight copy for distribution.

Best-practice compression workflow

1. Make a backup of the original PDF.
2. Try lossless cleanup when document behaviour matters.
3. Use recommended compression for image-heavy sharing copies.
4. Lower DPI or quality only when the result is still readable.
5. Use grayscale only when colour has no functional purpose.
6. Open the downloaded PDF and inspect every page.
7. Compare file size and confirm that the output actually solves the upload or storage problem.