How to Compress a PDF Without Losing Quality

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.

Compress your PDF now — free

No sign-up, no watermarks, no file size limits.

Compress PDF →

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.

Step-by-step: compressing a PDF with PDF99

The compression process using PDF99's online tool takes under a minute for most documents. Here's exactly what to do.

Upload your PDF by dragging it onto the upload area or clicking Choose File. The tool shows you a thumbnail of the file and its current size. Next, choose your quality setting using the slider. If you're not sure where to start, 75% is a safe default — it produces files that are typically 40-65% smaller than the original with no visible degradation at normal screen viewing size. If you need more reduction, try 60%. If quality is critical and you just want to strip metadata and reduce size slightly, try 85-90%.

The DPI setting controls how images are re-rendered. 150 DPI is the default and appropriate for most uses — screen reading, email, digital filing. If the PDF will only ever be viewed on screen and never printed, 96-120 DPI produces smaller files with no visible difference. If the PDF needs to be printed at A4 or larger, keep DPI at 150 or above.

Click Compress PDF and wait. For a 5-10 page document the process typically takes 5-15 seconds. For a 50-page scanned document it may take 30-60 seconds. When complete, the result shows you the new file size and the percentage reduction achieved. If the result is acceptable, click Download.

When compression doesn't reduce the file size much

You've run a PDF through the compressor and it barely got smaller. This happens for several specific reasons. The most common is that the PDF was already optimised when it was created — modern PDF creation software applies compression automatically on export. If your file came from Google Docs, Notion, or a current version of Word, it's probably already compact. Running it through a compressor will make it slightly smaller but not dramatically so.

The second reason is that the file contains mostly vector graphics and text rather than raster images. Text in a PDF compresses extremely efficiently and is rarely the cause of large files. If your large PDF contains mostly typed content with simple graphics, the reduction you'll get from compression is modest.

Third: the images inside the PDF may already be JPEG-compressed at a quality level similar to what you're targeting. Re-encoding a JPEG that's already at 70% quality to 70% quality produces minimal size change with a small additional quality loss. If your PDF is already well-compressed and you need it significantly smaller, you're at the practical limit of what compression can achieve without making the output look poor.

Compressing to a specific file size target

Some upload portals are very specific about file size limits — 200KB, 500KB, 1MB. Manually adjusting the quality slider and re-running compression until you hit the target is tedious. PDF99 has dedicated tools for the most common targets: compress to 50KB, compress to 100KB, compress to 200KB, and compress to 500KB. Each tool automatically searches for the right quality setting to hit the target without you needing to experiment manually.

Compressing PDFs on mobile

The PDF99 compression tool works in any mobile browser — Safari on iPhone, Chrome on Android. The process is identical to desktop: open the URL, upload your file from your phone's storage or cloud drive, adjust settings, and download. For detailed iPhone-specific steps including the Print to PDF method, see How to reduce PDF size on iPhone.

Keeping quality where it matters

The final thing worth saying about compression: always check the output before sending it anywhere important. Download the compressed file, open it, and check a few pages — particularly any pages with photographs, fine print, or detailed graphics. Zoom to 100% in your PDF viewer. If it looks good at that zoom level, it will look fine in normal use. If you see pixelation or blurring that bothers you, go back and try a higher quality setting. The goal is the smallest file that still looks acceptable for the purpose. For a document that will be read on screen at normal size, you can usually compress more aggressively than you'd think.