How to Reduce PDF File Size Without Ruining Quality
Last updated: 26 October 2026
Email attachments are often capped at 20–25MB and many job portals and government forms accept only 2–5MB. Here is why PDFs grow so large and how to shrink them without making them unreadable.
Why some PDFs are so large
A PDF that contains only text is usually tiny — a 20-page report can be under 200KB. Size balloons when the file contains images, and especially when those images are stored at a much higher resolution than they will ever be viewed at. A phone photo inserted into a Word document can easily carry 12 megapixels of data even though it is shown at the size of a postcard.
Scanned documents are the other big culprit. A scanner set to 600 DPI in colour produces a full-resolution image for every page, so a 10-page scan can reach 30–50MB. Embedded fonts, duplicated resources from repeated merges, and leftover editing data add smaller amounts on top.
What compression actually does
PDF compression mainly works on the images inside the file. It reduces their resolution to something appropriate for screen viewing or printing (downsampling) and re-encodes them with more efficient JPEG settings. Text and vector graphics stay sharp because they are not images at all — which is why a compressed text document still looks crisp when you zoom in.
Choosing a compression level
Low compression: best when the PDF will be printed or contains detailed photos or diagrams. Expect a modest reduction.
Recommended / medium: the right choice for most documents being emailed or uploaded. Images remain clear on screen while the file shrinks substantially.
High / extreme: use when you must meet a strict limit such as 1–2MB. Photos may look soft, but text stays readable.
Step by step
Open the Compress PDF tool and add your file.
Start with the recommended level and download the result.
Open the compressed file and zoom to 100% to check that text and any signatures are still clear.
If it is still too large, run the original (not the already-compressed copy) again at a higher level — compressing twice degrades quality faster than a single stronger pass.
Tricks when compression isn't enough
Scan at 150–200 DPI and in greyscale for text documents; colour 600 DPI scans are rarely necessary.
Remove pages you don't need with Split PDF or the PDF Editor before compressing.
If a form asks for several documents, compress each one separately rather than merging first.
For photo-heavy documents, compress the images first with Compress Image, then build the PDF with JPG to PDF.