What is the Compress PDF tool?
This is a size reducer for PDF files. You give it one document, tell it how aggressive to be, and it writes out a lighter copy. Because it runs entirely inside the page you are reading, you can compress PDF online free as often as you like — no account, no queue, no upload progress bar, and nothing stamped on the result.
Almost every oversized PDF is oversized for the same reason: photographs. A phone-scanned contract or a slide deck full of screenshots carries images at far higher resolution than any screen or printer will ever use. The tool goes after exactly that. It finds the embedded JPEG images, redraws them at the resolution you ask for, re-encodes them at the quality you ask for, and leaves the text, the vector graphics and the links alone. That is how a file gets dramatically smaller while still reading like a normal document.
Alongside the images it also cleans up the plumbing: metadata, embedded page thumbnails and — if you want — annotations and form fields are dropped, and the remaining objects are packed into compressed object streams. If the photos are already lean, that structural pass alone is often worth a few percent. And because the same code builds the preview, the estimate and the download, the "after" you see is the file you get.
How to reduce PDF file size online
- Drop one PDF onto the upload area at the top of the page, or click it to browse.
- Pick a preset under Optimise for — Web, Print or Email. Each one just fills in the controls below, which you are free to change.
- Choose a Compression method: keep text and re-save, downsample images only, or rasterise every page.
- Set the target image resolution in DPI and drag the JPEG quality slider until the After preview still looks acceptable.
- Press Estimate size to see what you will actually save before committing.
- Hit Compress PDF — the smaller copy downloads with -compressed added to the file name.
Key features
- Three honest methods — “Keep text (re-save)” touches no pixels, “Downsample images only” shrinks the photos, “Rasterise everything” flattens each page to one JPEG.
- One-click presets — Web (150 DPI, quality 70), Print (300 DPI, quality 88) and Email (110 DPI, grayscale, flattened) as sensible starting points.
- Exact DPI and quality control — any resolution from 36 to 600 DPI and any JPEG quality from 20% to 95%, not vague “low / medium / high” buckets.
- Before/After page preview — switch the viewer between the original page and the compressed one at the current settings, so you judge the loss with your own eyes.
- Size estimate up front — for the re-save and image modes the figure is the real output size; for rasterising it is projected from a few sampled pages.
- Optional grayscale — dropping colour is a big win on scanned text and costs nothing on a black-and-white original.
- Cleanup switches — strip metadata, remove embedded thumbnails, discard annotations and forms, and pack objects into compressed streams.
Benefits of using this PDF compressor
- Your document stays yours. The file is read, rewritten and saved by your own browser, so a payslip or a signed contract never crosses the network.
- No cap on files or file size. Compress one document or forty in a row; the only real limit is how much memory your device has.
- Searchable text survives. Two of the three methods never rasterise, so you can shrink a PDF and still select, copy and search the words in it.
- It refuses to make things worse. If a re-encoded image would come out larger than the original, the original is kept — so quality is never spent for nothing.
- Clean output. No watermark, no “compressed with…” footer, no email address required to download.
Who should use this tool?
Students with an upload limit
Submission portals love to cap attachments at 5 or 10 MB, and a scanned lab report blows straight past that. Use the Web preset, drop the DPI to around 120, and check the After preview to be sure the handwriting is still legible before you send it.
Office and admin staff fighting the mail server
When a 40 MB proposal bounces back from a client's inbox, the Email preset is the shortcut: lower resolution, grayscale and flattened pages, with annotations stripped so old comment threads do not travel with the file. For an internal version that must stay searchable, switch to the images-only method instead.
Job applicants uploading a CV
Recruitment sites are notorious for small size limits and silent failures. A CV exported from a design tool often carries an oversized headshot; downsampling images only usually gets you under the limit while keeping your name and contact details selectable — which matters, because many applicant tracking systems read the text rather than the picture.
Anyone archiving paper scans
A hundred pages photographed at full sensor resolution is enormous and no more readable than the same pages at 150 DPI in grayscale. Compress them once, keep the estimate as your guide, and store a copy that opens instantly instead of one that stalls every viewer you own.
Frequently asked questions
How do I make a PDF smaller for email?
Load the file, choose the Email preset and press Estimate size. If it is still too big, lower the DPI or the JPEG quality a little and estimate again. Most mail servers accept 10 to 25 MB, so aim comfortably under whichever limit you are up against.
Can I compress a PDF without losing quality?
Choose “Keep text (re-save)”. That method never touches a pixel — it only drops metadata and thumbnails and repacks the file's internal objects, so the result is visually identical. Savings are modest, typically a few percent up to about a quarter, because the images are left exactly as they were.
Why did my file barely shrink at all?
Because there was little to remove. The image mode only rewrites embedded JPEG streams; a PDF made of pure text and vector graphics has none, and an already-optimised file has small ones. The status line tells you how many images were rewritten and how many used a different format and were skipped.
Does the text stay selectable after compression?
With the re-save and images-only methods, yes — the text objects are copied through untouched. “Rasterise everything” turns each page into a picture, which gives the smallest file but destroys searchable text, links and form fields. Run the OCR tool afterwards if you need the text back.
Are my files uploaded to your server?
No. There is no server involved in the compression at all: pdf-lib and pdf.js do the work in your browser tab and your browser saves the finished file. Load the page once and it will keep working with your Wi-Fi switched off.
Is there a file size limit?
No fixed limit is imposed, but everything happens in RAM. A few hundred megabytes is fine on a desktop; on an older phone a very large scan may run out of memory, in which case split the document first and shrink the halves separately.
Can this PDF compressor handle a password-protected file?
Not reliably. Encrypted PDFs are flagged with a warning when you load them and compression may fail or drop content. Remove the password with the Unlock PDF tool first, then compress the unlocked copy.
What DPI and quality should I actually pick?
150 DPI at 70% quality is a good default for anything read on screen, and 300 DPI at 88% keeps photographs safe for printing. Below roughly 100 DPI small print starts to smear — the After preview is the fastest way to see where that line falls for your document.
Related tools you might need
Got a file that is too big to send? Scroll up, drop it in and compress PDF online free — the estimate tells you the result before you commit.
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