Guide
How to Compress a PDF (Reduce PDF File Size)
How to shrink a PDF so it fits an email or upload limit, without turning the text into a blurry image. Covers why PDFs get large, what actually reduces the size, and a free step-by-step method that runs in your browser.
TL;DR
- Almost all PDF bloat comes from embedded images. Recompressing those images is what actually reduces PDF size — everything else is rounding error.
- Free way: Compress PDF recompresses the embedded images entirely in your browser — no upload, no account, no watermark.
- Expect 30–70% smaller for scans, photo reports, and Canva or PowerPoint exports on the Balanced preset. Expect almost nothing for text-and-vector PDFs — those are already small.
- Never use a "compressor" that rasterizes each page into a picture. It shrinks the file but destroys selectable text, search, and copy-paste.
- If one file still will not fit, splitting it into parts with Split PDF is often a better answer than compressing harder.
- Adobe Acrobat Pro, Smallpdf, and macOS Preview can all do this too — an honest comparison is below.
PDF files grow large surprisingly fast. A scanned contract, a report with product photos, or a deck exported from Canva can easily top 10 MB — past most email attachment limits and past what many web upload forms accept. Compressing a PDF fixes that, and done properly it costs you nothing you will notice: the text stays selectable, the links keep working, and the document still looks right when printed.
Why PDFs Get Large
Almost all PDF bloat comes from embedded images. When you export from a design tool or scan a paper document, the images are stored as raw JPEG or PNG data inside the file, often at far higher resolution than anyone will ever view them at. A single full-page scan can add several megabytes on its own. Text and vector graphics are the opposite — PDF stores them as font glyphs and mathematical path descriptions, which are tiny.
- Scanned documents: every page is a full-resolution photograph, typically 200–300 dpi at A4 or Letter size.
- Presentation and design exports: slides from PowerPoint, Keynote, or Canva embed background images and graphics at high pixel counts.
- Reports and catalogues: product photography, charts saved as images, and full-bleed cover art all add up quickly.
- PDF/A archives: archival PDFs embed complete font subsets and colour profiles, adding overhead even with no images at all.
This is why the most useful diagnostic is simply asking what is inside your PDF. If it is mostly pictures, compression will help a lot. If it is mostly text, it will not help much — and no tool can change that, however aggressive its settings sound.
What PDF Compression Actually Does
A compressor that preserves quality works at the image level, not the page level. It walks the PDF looking for embedded raster images, re-encodes each one at a lower JPEG quality — discarding fine detail that is invisible at normal reading distance — optionally scales it down if it is far larger than the target resolution, and writes the smaller version back in place. The result is a structurally identical PDF: same pages, same text, same fonts, same links, same form fields. Only the image data changed.
Avoid any tool that "compresses" by rasterizing every page into a single flat picture. It does produce a smaller file, and it is how some free converters get their impressive-sounding numbers, but it destroys everything that makes a PDF useful: text is no longer selectable or searchable, copy-paste stops working, screen readers cannot read it, and the page goes soft the moment anyone zooms in. A good compressor never converts a page to a bitmap.
How to Compress a PDF — Step by Step
- 1
Open the Compress PDF tool
Go to Compress PDF on WeConvertIt. It runs entirely in your browser — no sign-up, and your file is never uploaded.
- 2
Drop in your PDF, or a whole batch
Drag one or more PDFs onto the drop zone, or click to browse. Each file in a batch is compressed independently with the same settings.
- 3
Choose a compression level
Light (85% quality, 2400 px cap) for near-original fidelity. Balanced (75%, 1800 px) for the best everyday size-to-quality trade-off. Maximum (60%, 1200 px) when file size is what matters most.
- 4
Click Compress
The tool finds every embedded JPEG, recompresses it, and rebuilds the document with pdf-lib. Text, fonts, hyperlinks, and vector artwork are untouched.
- 5
Check the numbers, then download
The result shows the before and after sizes, the percentage saved, and how many images were recompressed. Download the file, or grab a whole batch as one ZIP.
Which Preset Should You Use?
| Preset | Quality / max dimension | Typical reduction on an image-heavy PDF | Best for |
|---|---|---|---|
| Light | 85% / 2400 px | Around 15–35% | Portfolios, print-bound documents, anything where photo detail matters |
| Balanced | 75% / 1800 px | Around 30–70% | The default choice — email attachments, uploads, general sharing |
| Maximum | 60% / 1200 px | Around 50–85% | Strict size limits, screen-only reading, archiving a reference copy |
Those ranges assume an image-heavy PDF. A text-and-vector document will land near zero on every preset, and that is the honest answer rather than a fault in the tool.
How to Hit a Specific Size Limit
- Work down through the presets rather than starting at Maximum — Balanced clears most email limits on its own, with noticeably better-looking images.
- Remove pages you do not need to send. Split PDF extracts just the relevant range, and dropping half the pages halves the size with no quality cost at all.
- If you assembled the PDF yourself from images, resize those images first — Compress Image followed by Image to PDF gives you far finer control than compressing the finished PDF.
- For a very long scanned document, accept that there is a floor. A 200-page scan contains 200 page images; below a certain size they simply stop being legible.
Compression Tools Compared
| Tool | Cost | Uploads your file? | Notes |
|---|---|---|---|
| Compress PDF (WeConvertIt) | Free, no account | No — runs in your browser | Three presets, batch support, text and vectors left intact. No custom quality slider or exact target-size box. |
| Adobe Acrobat Pro | Paid subscription | No — desktop app | The most control available: per-image-type downsampling rules, font subsetting, and an optimizer that audits exactly what is taking up space. Overkill for one email attachment, excellent for production work. |
| Smallpdf / iLovePDF | Free tier, then paid | Yes — server-side | Convenient and effective, but your document goes to their servers and the free tier caps how many files you can process per day. |
| macOS Preview | Free, built in | No — local app | Export with the Reduce File Size Quartz filter. One fixed setting, no control, and often noticeably harsh on images — fine in a pinch. |
| Ghostscript (command line) | Free, open source | No — local | Fully scriptable with exact dpi and quality control. Genuinely powerful if you are comfortable in a terminal, and the right answer for automating hundreds of files. |
If you need to hit an exact byte target, or apply different rules to different image types within one document, Acrobat Pro or Ghostscript will get you there with a precision this tool deliberately does not expose. For the ordinary case — a file that needs to fit an email, without the document leaving your laptop — the in-browser route is faster and more private.
What to Do After Compressing
If you are assembling a document from several sources, compress last: merge the files first with Merge PDF, then compress the finished document once. If the PDF needs to stay confidential on the way to its recipient, add a password with Protect PDF after compressing, since an encrypted file cannot be compressed. And if what you actually need is images rather than a document, convert the PDF to JPG instead of shrinking it.
Frequently Asked Questions
How do I reduce the size of a PDF file?
Recompress the images inside it. Open the PDF in a compressor such as Compress PDF, pick a compression level, and download the result — the tool re-encodes each embedded JPEG at a lower quality and, if an image is far larger than it needs to be, scales it down. Text, fonts, hyperlinks, and vector graphics are left untouched, so the document still behaves like a PDF afterwards.
How can I compress a PDF for free?
Compress PDF is free with no sign-up, no watermark, no daily file cap, and no upload — it runs in your browser. macOS users also have a built-in option (open in Preview, then Export with the Reduce File Size Quartz filter), though it is aggressive and often visibly degrades images. Smallpdf and iLovePDF have free tiers too, but they upload your file and limit how many documents you can process per day.
Why is my PDF still large after compressing it?
Usually because there was not much image data to remove. A PDF full of text, tables, and vector diagrams is already stored compactly — as font glyphs and mathematical shapes rather than pixels — so an image compressor has little to work on. The other common case is a PDF whose images were already compressed hard before being embedded; re-encoding them again saves very little. The tool reports how many embedded images it found and how many it recompressed, which tells you immediately which case you are in.
Does compressing a PDF reduce quality?
It reduces image quality, by design — that is where the savings come from. Text, fonts, and vector artwork are not affected at all and stay perfectly sharp at any zoom level. On the Light preset (85% quality) the difference in the images is very hard to see; on Maximum (60% quality, 1200 px cap) it is visible if you zoom into a photo. Pick the preset that matches how the document will actually be viewed.
How do I compress a PDF to under 1 MB for email?
Start with the Balanced preset and check the resulting size — the tool shows before and after. If it is still too big, re-run the original on Maximum. If it is still too big after that, the file is probably long rather than image-heavy: use Split PDF to send it in parts, or share a link instead of an attachment. Getting a 200-page scanned document under 1 MB is usually not achievable without making the pages unreadable.
Can I compress a password-protected PDF?
Not directly — an encrypted PDF cannot be modified until it is decrypted. Remove the password first with Unlock PDF, compress the unlocked copy, then re-apply protection with Protect PDF if you still need it. See the password protection guide for that last step.
Is it safe to compress a PDF online?
It depends entirely on whether the tool uploads your file. Most online PDF compressors send your document to a server, process it there, and send it back — a real consideration for contracts, medical records, or anything confidential. Compress PDF does the work in your own browser tab using pdf-lib; you can confirm nothing is transmitted by opening DevTools and watching the Network tab while you compress.
Can I compress several PDFs at once?
Yes. Drop a whole batch onto the tool — each file is compressed independently with the same settings, and you can download the results one by one or as a single ZIP.