How to reduce PDF file size without losing quality
What actually makes a PDF heavy, which compression settings keep text and images sharp, and the free methods that work on Windows, Mac and phones.
Compress PDF filesFree · No sign-up · No watermark Try it now“Without losing quality” is the promise on every PDF compressor, and it’s only half true. The honest version: you can usually make a PDF much smaller with no visible loss — as long as you know where the weight comes from and which settings to choose. This guide explains what’s inside a heavy PDF, what each compression level really does, and how to get the best result with free tools on Windows, Mac, iPhone and Android.
If your goal is simply to get under an email limit, our shorter guide on making a PDF small enough to email lists the limits of Gmail, Outlook and iCloud.
What makes a PDF heavy
A PDF is a container. Its size depends on what’s packed inside:
| Content | Typical weight | Compressible? |
|---|---|---|
| Text | A few KB per page | Already compact |
| Embedded fonts | 20 KB – 1 MB per font | A little (subsetting) |
| Vector graphics (charts, logos, CAD) | Small to medium | Rarely |
| Photos and scanned pages | 0.3 – 5 MB per page | Yes, a lot |
| Metadata, thumbnails, edit history | Small, sometimes duplicated | A little |
In practice, images account for most of the size of almost every large PDF. A colour scan at 300 dpi stores millions of pixels per page; a PowerPoint export keeps every photo at its original camera resolution even when it appears as a thumbnail. Compression tools win their big percentages by resampling and re-encoding those images — not by squeezing text.
Lossless vs lossy: what “without losing quality” means
- Lossless optimization rewrites the PDF more efficiently: removes duplicated images and fonts, unused objects and leftover edit history, compresses internal streams. Nothing visible changes. Gains range from nothing to 10–30% on badly produced files.
- Lossy image compression lowers image resolution (dpi) and re-encodes them as JPEG at a chosen quality. This is where 50–90% reductions come from on scans. It’s technically “loss”, but at the right resolution the human eye can’t tell on screen.
The trick is choosing a resolution that matches how the PDF will be used:
| Use | Resolution that looks sharp | Compression level in TurboConvert |
|---|---|---|
| Reading on a phone or laptop, email | ~72–100 dpi is enough for most | Strong — smallest file |
| Screen reading with zoom, office printing | ~150 dpi | Recommended — good quality |
| Professional or high-quality printing | ~300 dpi | Light — best quality |
Text and vector graphics are not resampled, so even the strongest level keeps letters crisp. What you lose at the strong level is fine detail in photos — visible if you zoom into a picture, rarely when reading.
The quickest method: compress in your browser
Compress PDF runs Ghostscript — the open-source engine used by many professional PDF tools — directly in your browser:
- Click Choose files or drop one or more PDFs (up to 200 MB each).
- Choose a Compression level. Start with Recommended — good quality.
- Click Convert. The smaller PDF downloads automatically.
- Open it and zoom on a photo and on the smallest text. If it’s fine and you need smaller, try Strong; if you see artefacts, use Light.
Because nothing is uploaded, it’s suitable for confidential documents. The first run downloads the compression engine (a few seconds); later runs start instantly. If the file can’t be made smaller, your original is kept rather than replaced by a bigger one.
Free built-in methods, system by system
Mac: Preview, with a better filter
Preview’s File > Export > Quartz Filter > Reduce File Size is free but aggressive: it can make scans blurry or blocky. For better control, open ColorSync Utility (Applications > Utilities), go to Filters, duplicate Reduce File Size and raise the image quality and resolution (around 150 dpi). Your custom filter then appears in Preview’s export menu. Always keep the original — Preview can overwrite it if you use Save instead of Export.
Windows: fix the source
Windows has no built-in tool to shrink an existing PDF. “Microsoft Print to PDF” re-creates a file but doesn’t reliably reduce it, and it drops clickable links. The best free approach on Windows is to create a lighter PDF in the first place (see below) or use a browser-based compressor.
Word, PowerPoint and Excel: export with the right settings
When you control the source document, you’ll get a better result by exporting correctly than by compressing afterwards:
- Word (Windows): File > Save As > PDF, select Minimum size (publishing online) for email, or Standard for print.
- PowerPoint: File > Compress Pictures (or Picture Format > Compress Pictures), choose 150 ppi, tick “Delete cropped areas”, then export.
- Any Office app: paste images at the size you need instead of full-resolution camera photos.
iPhone and Android: rescan, don’t recompress
Most heavy PDFs made on phones are scans. In the iPhone Notes scanner or an Android scanning app, choose grayscale or black & white when colour isn’t useful — the file is often several times lighter, and usually easier to read. For PDFs you already have, a browser compressor works on phones too.
Extra ways to cut size without touching quality
- Remove pages you don’t need. Blank pages, duplicated annexes, cover sheets. Organize PDF shows page thumbnails so you can delete them, or use Split PDF to keep a page range.
- Don’t merge before you trim. If you’re assembling a file, compress the heavy scans, then merge — or merge and compress once at the end. Avoid compressing the same file twice.
- Flatten huge vector drawings only if you know what you’re doing: very complex maps or CAD exports can be lighter as images, but you lose infinite zoom.
- Don’t expect ZIP to help. PDFs are already compressed internally; zipping saves a few percent at best.
When compression is the wrong answer
- Text-only PDFs of 1–3 MB are mostly fonts and text; there’s little to gain. Splitting or sending a link works better.
- Print-ready files for a printer or publisher must keep 300 dpi images and specific colour settings. Don’t compress them — send a link.
- Signed PDFs with a digital (certificate) signature: any rewrite of the file invalidates the signature. Compress before signing, never after.
- Archival PDFs (PDF/A): a compressor may not preserve PDF/A compliance. If compliance is required, use a tool that explicitly validates PDF/A.
Quality checklist after compressing
- Zoom to 200% on the smallest text: it should be as crisp as before.
- Look at photos, signatures and stamps: no blocky artefacts around edges.
- Search for a word (Ctrl/Cmd+F): if it was searchable before, it still should be.
- Click a link and check bookmarks if the file has any.
- Compare the sizes — and keep the original until the recipient confirms they can read it.
Which approach for which file?
| File | Expected gain | What to do |
|---|---|---|
| Colour scan, 300 dpi | Often 70–90% | Compress, Recommended or Strong |
| PowerPoint export with photos | Often 50–80% | Compress pictures in PowerPoint, re-export, or compress the PDF |
| Word report, mostly text | 0–20% | Usually already fine; export with Minimum size if needed |
| Photo book or brochure for print | Keep quality | Don’t compress; send a link |
| Already compressed PDF | Minimal | Use the original, not a second pass |
Need to go the other way — turning photos into a compact PDF? JPG to PDF combines images into one document; run the result through Compress PDF if it’s heavy.