PDF Compression Levels Explained: Low, Medium, High

PDF compression levels control the tradeoff between file size and visual quality. Most compressors offer three settings — Low, Medium, and High — but few explain what actually changes at each level. Pick the wrong one and you either get a file that's still too large or a document that looks blurry and unprofessional. This guide breaks down what each compression level does, when to use it, and how to hit the right file size target for your situation.

What PDF Compression Actually Changes

PDF compression targets two things: images and redundant data.

Images are almost always the largest component of a PDF. A 25 MB file is usually 22 MB of images and 3 MB of text and structure. Compression re-encodes those images at lower resolution (DPI) and higher JPEG compression. Text and vector graphics are already compact and stay sharp — compression doesn't touch them.

Redundant data includes embedded font subsets that duplicate characters, unused metadata, embedded thumbnails, and duplicate image objects. Compression strips these out.

The three compression levels differ in how aggressively they re-encode images and what they strip.

The Three Compression Levels Compared

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Low Compression

Low compression applies minimal re-encoding. Images are downsampled modestly — typically from 300+ DPI to around 200 DPI — and JPEG quality stays high (around 80%). Redundant metadata is stripped, but fonts and image data are largely preserved.

File size reduction: ~30%
Visible quality loss: Minimal to none
Best for: Archival, print-ready documents, high-quality client deliverables

Use Low when quality matters more than size — portfolios, design proofs, documents headed for print.

Medium Compression

Medium is the default for most users. Images drop to roughly 150 DPI with JPEG quality around 60%. This is the sweet spot where file size shrinks dramatically while text stays crisp and images remain acceptable on screen.

File size reduction: ~60%
Visible quality loss: Slight softening of images, text unaffected
Best for: Email attachments, web downloads, general sharing

Medium is what you want for most business documents — reports, proposals, invoices sent by email.

High Compression

High compression is aggressive. Images drop to 72–100 DPI with JPEG quality around 40%. Photos become noticeably softer, but text remains sharp because it's vector-based, not rasterized.

File size reduction: ~80%
Visible quality loss: Clear on images, minimal on text
Best for: Email with strict size limits, web preview, mobile viewing

Use High when you're fighting a hard size cap — a 25 MB email limit or a 5 MB upload form. The text stays readable; the images take the hit.

Image vs Text Compression Impact

A key point: compression levels affect images, not text. PDF text is stored as vector glyphs with embedded font references. It doesn't have pixels to downsample. Whether you choose Low or High, your text stays razor-sharp at any zoom level.

What changes is the imagery:

Photos — lose detail and gain JPEG artifacts at higher compression
Scanned pages — soften, since the entire page is one image
Charts and diagrams — if rasterized, they blur; if vector, they stay sharp

This is why a text-heavy report compresses beautifully at High with no visible loss, while a photo-heavy brochure looks degraded at the same level.

DPI Reduction Explained

DPI (dots per inch) determines how many pixels make up an image. A 4×6 inch photo at 300 DPI is 1200×1800 pixels. At 72 DPI, it's 288×432 — roughly 7% of the pixel count.

300 DPI — print quality, large file
150 DPI — screen quality, readable on any device
72 DPI — web/email quality, smallest file

Compression levels map to DPI targets. Low keeps images near their source DPI. Medium targets 150. High targets 72–100. For more detail on keeping quality intact, see our compress pdf without losing quality guide.

When to Use Each Level

Situation	Recommended Level	Target Size
Print-ready document	Low	Under 25 MB
Email attachment	Medium	Under 10 MB
Web download	Medium	Under 5 MB
Strict email limit	High	Under 2 MB
Mobile preview	High	Under 1 MB
Archival storage	Low	Original quality

File Size Targets by Use Case

Knowing your target size before compressing saves trial and error:

Gmail attachment limit: 25 MB — Medium usually gets you there
Outlook default limit: 10 MB — Medium to High
Web form upload: varies, often 2–5 MB — High
Mobile data loading: under 1 MB — High
Print shop submission: under 25 MB at 300 DPI — Low

Start with Medium, check the output size, and step up to High only if you're still over your target.

Compress Your PDF Now

Ready to compress? Open the PDF compressor, add your file, choose Low, Medium, or High, and download the result — all in your browser. For a quick single-file shrink, try the compress PDF tool. No upload, no signup, and your text stays sharp at every level.