If you've ever tried to email a PDF and been told the file is too large, or watched a document take an age to open on someone's phone, you already know the problem. PDFs can get surprisingly large — especially ones with photos, scanned pages, or complex graphics.
The good news: most PDFs can be made significantly smaller without any visible change in quality. Here's how to do it properly.
Why do PDFs get so large?
A PDF is a container format. It holds text, images, fonts, metadata and structural information. The main contributors to file size are:
- Embedded images — especially high-resolution photos. A single full-resolution JPEG can add several megabytes.
- Scanned documents — these are essentially just images in a PDF wrapper. A 50-page scanned document is 50 images.
- Embedded fonts — PDFs often embed the complete font file, adding 200–400 KB per font.
- Metadata and revision history — some PDF editors embed thumbnails, revision history, form data and print settings that aren't needed in the final file.
Method 1: Use PDF99 Compress
The fastest method is to use our free online Compress PDF tool. Upload your PDF and the tool strips unnecessary metadata, redundant objects and embedded revision history. This is lossless — visual quality is unchanged.
This method works best on PDFs that have accumulated extra data over time — such as documents that have been through multiple rounds of editing in Word, Acrobat or other software.
Method 2: Reduce image resolution before creating the PDF
If your PDF was created from high-resolution photos, the images inside are probably far sharper than they need to be. For on-screen viewing, 96 DPI is plenty. For print, 150–300 DPI covers almost all needs.
If you're converting images to PDF, our JPG to PDF converter lets you choose the output page size and margins, which affects how images are scaled into the document. Choosing a standard page size with no margin produces a clean, reasonably-sized file.
Method 3: Print to PDF
On Windows or Mac, you can open a PDF and use File → Print → Save as PDF to create a new version. This re-renders the document through the OS PDF engine, which often strips embedded fonts, flattens layers and removes metadata. Results vary, but it's worth trying on stubborn files before using more specialised tools.
How much will it shrink?
It depends on the content:
- A text-heavy document with little imagery: 15–30% reduction
- A PDF with embedded photos: 30–60% reduction
- A heavily-edited document with revision history: sometimes 50% or more
- A PDF already optimised or created by modern software: minimal reduction
The only way to know is to try. Compression tools strip overhead data, not visual content — there's nothing to lose by running it.
What about online services that promise 80% reduction?
Be cautious. Aggressive compression often works by re-encoding embedded images at much lower quality. The file gets smaller but photos come out blurry and text near images looks softer. Check the output carefully before sending it anywhere important.
For most business and personal documents, a 20–40% reduction at full quality is more useful than a 70% reduction that makes the document look unprofessional.