How to Compress a PDF (Free & Online)

1vs Team Updated 2026-08-27 pdf-toolkit

Upload your PDF to PDF24 — open-source, fully free, no signup. Pick Recommended compression for email; skip Extreme on scanned pages.

Step-by-step

Choose a PDF compression tool

For unlimited free compression with no signup, use PDF24 — open-source, browser-based, and processes files up to 100MB. The PDF24 desktop app also works offline on Windows. For faster processing with 3 free tasks daily, Sejda delivers compressed files in under 10 seconds. For simple one-click compression, iLovePDF offers 2 free tasks per day with three quality presets.

Upload your PDF file

Drag and drop your PDF into the upload area or click to browse. PDF24 processes files locally in your browser — no data leaves your device, which matters for contracts and tax documents. iLovePDF uploads to cloud servers, so avoid it for sensitive files.

Select compression level

Most tools offer three compression levels. Sejda provides 'Extreme', 'Recommended', and 'Less' — 'Extreme' reduces file size by 60-80% and is not lossless (expect noticeable image softening), while 'Less' keeps near-original quality at 10-30% reduction. iLovePDF labels its presets as 'Extreme', 'Recommended', and 'Less Compression'. Pick 'Recommended' for email attachments — it balances size and readability. Do not use Extreme on scanned PDFs; raster pages already behave like images and Extreme can make text unreadable.

Click Compress and wait

Processing takes 5-15 seconds for a typical 10MB document. PDF24 runs locally so speed depends on your computer — larger files may take 30-60 seconds. Sejda uses cloud processing and finishes most files in under 10 seconds regardless of size.

Download the compressed PDF

Click the download button to save your compressed file. Compare the original and new file sizes — iLovePDF shows both sizes side by side after compression. If the result is still too large for a 25MB mailbox or a 5MB job portal, re-upload and select a stronger compression level, or split the PDF first. The original file stays untouched.

Verify the output quality

Open the compressed PDF in PDF24 or your preferred viewer and scroll through every page. Check that text remains sharp, images aren't pixelated, and fonts render correctly. For documents with charts or diagrams, zoom to 200% to catch quality loss. If quality is unacceptable, re-upload and use a lower compression level — Recommended, not Extreme.

Compress on a Mac with Preview (optional)

On macOS, open the PDF in Preview, choose File → Export, then Quartz Filter → Reduce File Size. Recheck photos and small type at 100% — Preview's filter is aggressive on images. If the result looks muddy, skip Preview and compress with PDF24 locally instead. Windows users can install the PDF24 desktop app for the same offline path.

Recommended Tools

PDF24

Fully free with no daily limits, open-source, processes locally for privacy

72 /100

Sejda

Fastest cloud processing, three compression levels, 3 free tasks per day

80 /100

iLovePDF

Clear quality presets, shows before/after file sizes, 2 free tasks daily

80 /100

FAQ

What is the best free tool to compress a PDF?

PDF24 is the best free option — no daily limits, no signup, no watermarks. Files process locally in your browser for privacy. Sejda (3 free tasks per day) and iLovePDF (2 free tasks per day) are cloud alternatives when you want speed over a local run.

How do I compress a PDF without losing quality?

Use Recommended, not Extreme. Recommended on Sejda or iLovePDF keeps near-original readability. Extreme is not lossless — images and diagrams soften. Always preview at 100% before you send the file. For scans, skip Extreme entirely.

How much can I reduce a PDF's file size?

Most PDFs shrink by 40-70% on 'Recommended' mode. 'Extreme' mode on Sejda cuts 60-80%, though images may lose quality. 'Less' stays closer to the original at about 10-30% reduction.

How do I compress a PDF for email?

Most mailboxes allow about 25MB; many job and school portals cap uploads around 5MB. Compress with PDF24 on Recommended first, then Extreme only if text still reads cleanly. If it is still over the cap, split the PDF and send parts.

Can I compress a PDF on my phone or iPhone?

Yes — iLovePDF and Sejda work in mobile browsers. On iPhone, open the file in Files, share it into Safari, then compress. The iOS Files app does not shrink PDFs by itself — you still need a compressor. Avoid uploading contracts from a public Wi-Fi session.

How do I compress a scanned PDF?

Do not use Extreme on scans. A scanned PDF is already a stack of images, so Extreme often blurs type and signatures. Start with Recommended in PDF24 or Sejda, then check every page. If the scan is huge, split the PDF or compress the source images first — see how to reduce image file size.

How do I compress a PDF offline for privacy?

Use PDF24 in the browser (local processing) or install the PDF24 desktop app — open-source, no account, no telemetry. Skip iLovePDF for medical, legal, or tax files (it runs in the cloud). Power users sometimes script Ghostscript or self-host Stirling PDF; those are not in our recommended list for this guide.

How do I compress a PDF on Windows?

Use PDF24 in any browser, or install the PDF24 desktop app for fully offline compression. Sejda also has a desktop build if you already use its 3-task free tier. Ghostscript is a command-line option for IT users, not a first-stop for this how-to.

How do I compress a large PDF (around 100MB)?

PDF24 is listed for files up to 100MB. If the file is still too big after Recommended/Extreme, split the PDF into sections, compress each part, then send or re-merge. Image-heavy exports (slides, scans) shrink more than text-only reports.

Can I compress a PDF in Adobe Acrobat?

Acrobat Pro has File → Save as Other → Reduced Size PDF (or Optimize PDF). That path is paid and vendor-owned. For a free online pass, PDF24 covers the same shrink-for-email job without a Creative Cloud seat.

Can I batch compress PDFs?

This guide is for one file at a time. PDF24 desktop can process multiple files if you already use the app; treat batch as a power-user extra, not the default. Cloud free tiers (Sejda 3/day, iLovePDF 2/day) are a poor fit for bulk jobs.

Best tools → ilovepdf vs pdf24 ilovepdf vs sejda pdf24 vs sejda split a pdf