How to Reduce PDF File Size Without Losing Quality
Short answer
Work out what is making the PDF large first. If it is scanned pages or photos, downsampling the images to 150 DPI is the fix and it does most of the work. On macOS use Preview's Quartz filters, on Windows re-export from the source document or print to PDF, and keep email attachments under 10MB to be safe.
On this page
Most advice about shrinking a PDF starts with a tool. That is the wrong order. A PDF containing thirty scanned pages and a PDF containing one chart with badly embedded fonts are the same problem on the surface and completely different underneath, and the fix for one does nothing for the other.
Spend two minutes working out what is taking up the space, and the right method becomes obvious.
If you already know your PDF is a scan, skip ahead — that case has its own guide, how to compress a scanned PDF, because none of the general methods below move the needle on it.
Work out why the PDF is large
Open the file and look at it, then use the page count as a rough calculator.
| Size per page | Almost certainly |
|---|---|
| Under 100KB | Text and vector graphics — already efficient |
| 200KB–1MB | Compressed photos, or embedded font subsets |
| 1–5MB | Print-resolution images, or colour scans |
| Over 5MB | Full-resolution scans, or uncompressed images |
Three specific culprits account for nearly everything:
Scanned pages. Every page is a photograph. A colour scan at 600 DPI is several megabytes per page before any text exists. This is the most common cause of a genuinely enormous PDF and the one with the most room to improve.
Print-resolution images. An export intended for a printing press keeps images at 300 DPI or higher. On a screen, anything above roughly 150 DPI is invisible detail you are paying for.
Embedded fonts. Each font family embedded in full adds a few hundred kilobytes. Usually minor — but a document assembled from many sources can carry a dozen fonts, and that adds up.
You can confirm which it is by checking the document properties (File → Properties in most viewers) and by zooming to 400% on an image: if it stays sharp, there is resolution to spare.
The best fix: re-export from the source
If you still have the original Word, Pages, PowerPoint or InDesign file, this beats every compression tool, because you are choosing settings before the information is thrown away rather than degrading an already-degraded file.
In Word, use File → Save as Adobe PDF or Export → Create PDF, and choose Minimum size / Standard (publishing online) rather than Best for printing. That single choice often cuts the file by half or more.
Also look at the images inside the document itself. Word can shrink them for you: select an image, then Picture Format → Compress Pictures, and pick Web (150 ppi). Tick Delete cropped areas of pictures — cropped-away pixels are still stored in the file until you do.
On macOS: Preview
Preview has a built-in compressor and it is genuinely good.
- Open the PDF in Preview.
- File → Export (not Save As).
- In the Quartz Filter dropdown, choose Reduce File Size.
- Save under a new name so you keep the original.
The caveat is that the default filter is aggressive — it targets a low image resolution, which is fine for a text document with a logo and too harsh for a photo portfolio. If the result looks poor, export again without the filter and try one of the other approaches below.
For scanned documents specifically, open the file in Preview, choose File → Export, set the format to PDF, and where your scanner software offers it, rescan in greyscale at 200–300 DPI rather than colour at 600.
On Windows: print to PDF
Windows has no direct equivalent of Preview’s filter, but the built-in Microsoft Print to PDF driver re-renders the document, which discards excess image data as a side effect.
- Open the PDF in any viewer.
- Press Ctrl+P.
- Choose Microsoft Print to PDF as the printer.
- Print, and save to a new filename.
This is lossy in a way you do not control, and it flattens forms, annotations and any text-selection layer — so it is a last resort for a document you only need to read or send, not for one you need to edit or search.
A better Windows option, if the PDF came from an Office file, is to go back to the source and re-export as described above. If it came from a scanner, use the scanner utility’s own settings rather than fixing it after the fact.
On iPhone and iPad
The Files app can do this without any additional app installed.
Long-press the PDF in Files, then look for Compress. That produces a zip archive rather than a smaller PDF, which helps for storage but not for a recipient who needs to open it directly.
For a genuinely smaller PDF, open it in Files, tap the share icon, and use Print — then pinch outwards on the print preview to open it as a PDF, and share from there. It is an odd workflow but it uses the same re-rendering path as print-to-PDF on a desktop.
If the PDF is one you created by photographing documents, the real fix is upstream: the Notes app’s document scanner produces far smaller files than photographing pages with the camera, because it detects edges and saves in a mode suited to documents.
Quality tradeoffs, honestly
There is no compression that removes size without removing something. What matters is whether you will notice.
| Change | Lossless? | Noticeable when |
|---|---|---|
| Strip metadata and duplicate fonts | Yes | Never |
| Subset embedded fonts | Yes | Never |
| Downsample images to 150 DPI | No | Printing, or zooming past ~200% |
| Downsample to 72 DPI | No | Immediately on any modern screen |
| Convert colour scans to greyscale | No | Only if colour carried meaning |
| Re-encode photos at lower JPEG quality | No | On large photos, in flat areas |
The practical rule: 150 DPI for anything that might be printed on an office printer, 96–120 DPI for screen-only documents, and never go below 72 DPI for a document anyone has to read.
If the PDF is mostly photographs and you need control over the tradeoff, extract the images, compress them deliberately, and rebuild the document. Our image compression guide covers the quality settings worth using, and the image compressor tool runs in your browser so nothing is uploaded.
Email size limits
This is the reason most people are here, so the numbers are worth stating plainly.
| Service | Attachment limit |
|---|---|
| Gmail | 25MB |
| Outlook.com | 20MB |
| Most corporate mail servers | 10–25MB |
| Safe for any recipient | Under 10MB |
Two things people get caught by. First, attachments are encoded for transport, which inflates them by roughly a third — a 24MB file can fail a 25MB limit. Second, the limit that matters is the recipient’s, and you cannot see it. A message can leave Gmail happily and bounce at the other end.
Above 10MB, share a link from Drive, OneDrive, iCloud or Dropbox instead. Gmail offers to do this automatically, and the recipient gets a working document instead of a bounce.
What to avoid
- Uploading confidential PDFs to free online compressors. Contracts, medical records, payslips and anything with a signature belong on your own machine.
- Compressing the same PDF repeatedly. Each pass re-encodes already-degraded images. Two rounds of compression look considerably worse than one.
- Zipping a PDF to email it. PDFs are already compressed internally, so a zip typically saves a few percent while making the file harder to open.
- Deleting pages to hit a size target when images are the problem. Fix the images and you keep the document intact.