PDFs grow fast. A scanned 30-page contract can balloon to 80 MB. A photo-heavy presentation runs into mail attachment limits. A textbook export is too big for a phone. Compression solves all three — by re-encoding the embedded images at a sane DPI and re-saving the PDF without the bloat.
Zebra compresses on its own server: your PDF travels over encrypted HTTPS, is compressed with Ghostscript, and streams straight back. Temporary files are deleted the moment processing finishes — nothing is stored, shared, or passed to a third party. It works the same on a Mac or an iPhone — you just drop the PDF in.
Three steps
- Open the PDF compressor.
- Drag your PDF into the dropzone (or click to pick one).
- Choose Light, Medium, or Strong, click Compress, then Download.
That's it. Most 10–30 MB PDFs finish in well under 30 seconds on a decent connection. If you also need to shrink the images themselves before they go into a PDF, check the guide to compressing JPG, PNG and WebP.
Why PDFs get big
Three things usually make a PDF heavy:
- Embedded raster images at print DPI. A single 300-DPI A4 scan is roughly 2480×3508 pixels. Multiply by 30 pages and you're at 80 MB — most of it pixels nobody can see on a phone.
- Uncompressed or weakly compressed image streams. Some PDF creators store images as raw or with low-quality DEFLATE compression. Re-encoding them as JPEG at 85–98% quality typically halves the page size with no visible loss.
- Embedded font subsets bundled multiple times. A common Word-to-PDF bug. Less impact than images but real.
Zebra targets the first two. On the server, Ghostscript re-encodes the embedded images at the quality level you chose and rewrites the file without the bloat. Text stays as text — searchable, selectable, copy-pasteable.
Light, Medium, Strong — what each preset does
Each preset trades image detail for file size. Here's what to expect:
| Preset | Best for | Typical savings |
|---|---|---|
| Light | Print, archives, zoom-in review | 10–30% |
| Medium | Everyday documents (default) | 40–60% |
| Strong | Email, web, mobile | 60–80% |
Light is visually lossless. Use it for documents you'll print, archive, or send to a client who'll zoom in.
Medium is the default. The output is still print-grade. Pick this unless you have a specific reason not to.
Strong is for email, web sharing, and mobile. Images stay sharp on screen and crisp enough for low-stakes print. This is where you'll see the dramatic 60–80% drops.
What happens to your file
Zebra compresses PDFs on its own server — that's where Ghostscript, a professional-grade compression engine, can do the best job. Here is exactly what happens to your file:
- Encrypted in transit. The upload and the download both travel over HTTPS. Nobody on the network can read the file.
- Deleted right after processing. The server keeps temporary files only for the duration of the compression and removes them as soon as the result streams back to you.
- Never stored, never shared. No archive, no third party in the pipeline, and nothing is used for training.
If a document is so sensitive that it must not touch any server — even briefly, even encrypted — use an offline desktop tool instead. For everything else, the file is on our server for seconds and then gone.
When NOT to compress
Compression is lossy on the image streams (text is preserved). A few cases where you should skip it or pick Light. If your PDF is large because of one or two high-resolution images, sometimes it's faster to crop them down to size before re-bundling — then compression on the leaner PDF wins twice.
- PDF/A archival files. Long-term archive PDFs are meant to be byte-stable. Don't compress them.
- Already-optimized small PDFs. If your file is under 1 MB and mostly text, there's nothing to gain. Zebra will detect this and show "0% change" instead of pretending to compress.
- High-detail technical drawings. CAD exports, dense schematics, microscope images — pick Light, or compress the source images separately before exporting.
- Master files for print. Keep the master at full DPI. Compress a copy for email.
Zebra vs Smallpdf vs iLovePDF
A practical comparison, as of May 2026:
| Feature | Zebra | Smallpdf | iLovePDF |
|---|---|---|---|
| Where it runs | Server (Ghostscript) | Server | Server |
| Files after processing | Deleted immediately | Deleted per policy | Deleted per policy |
| File size limit (free) | 150 MB | 5 MB | 15 MB |
| Daily limit (free) | 2 / day (anon), 3 / day (signed in) | 2 / day | Limited |
| Watermark | No | No | No |
| Signup required | No | No (small files) | No (small files) |
| Three quality presets | Yes | Limited | Yes |
The honest summary: if your PDF is over 5 MB or doesn't fit in iLovePDF's 15 MB free cap, Zebra is the cleaner path. For tiny files under 5 MB you can use any of the three.
Troubleshooting
"Compression failed"
Usually one of: a password-protected PDF (decrypt it first in Preview on Mac or Adobe Reader), a corrupted PDF the compressor can't parse, or a connection drop during the upload. Check that the file opens normally, then try again.
The result is barely smaller
Three possibilities: the PDF is already optimized (text-only or pre-compressed images), the images are tiny vector logos that don't benefit from re-encoding, or you picked Light on a file that needed Strong. Try Strong and compare.
The text looks fine but images are blurry
That's expected on Strong with photo-heavy PDFs. Switch to Medium — photos stay sharp on screen and even print acceptably.
It's slow on my phone
On a phone the bottleneck is upload speed, not your device — the compression itself runs on Zebra's server. A 30 MB PDF on slow mobile data takes a while to upload; switch to Wi-Fi if you can. As a fallback, the iOS Files app has a built-in "Reduce File Size" action (lower quality, but it runs entirely on the device).