Compress a PDF Online: Free, With Real Quality Controls

A PDF you need to send is too large for the email attachment limit, or too large for the upload box on whatever portal is asking for it. The fix is to compress, but most browser-based compressors give you three buttons (Low / Medium / High) and no actual control, while the desktop tools that do have controls cost money and need installation.

Signegy compresses PDFs in your browser with real quality controls — a JPEG quality slider, a DPI slider, and a result banner that tells you the actual before/after sizes so you can iterate until you hit your target. There’s an honest trade-off baked into the approach (text becomes non-selectable), and we tell you about it on the empty state, on this page, and in the FAQ. Most online compressors don’t.

How It Works

1. Drop your PDF onto the tool above. The tool reads the file size and renders the first 12 pages as previews.
2. Adjust the quality and DPI sliders to your taste. Defaults work well for typical email-attachment use; lower both for aggressive compression, raise both if quality matters more than file size.
3. Click “Compress & Download”. Each page is re-rendered to canvas at the chosen DPI, encoded as JPEG at the chosen quality, and embedded in a new PDF. The result downloads with a name like [original]-compressed.pdf, and the banner above the previews shows the size change.

The compression runs entirely on your CPU — no upload, no waiting in a queue, no third party touching your file. For a typical 10MB document the operation takes a few seconds; for very large files it scales with your machine, not our servers.

The Sliders, Explained

DPI controls how many pixels each page is rendered at before compression. The default is 108 DPI (1.5x scale), which matches typical screen reading without being excessive. 72 DPI is “screen-only” — fine if the recipient will only view it; pixelation is visible if printed. 216 DPI is “print quality” — looks sharp printed but produces larger files. Going above 216 rarely helps; you’re rendering at higher than typical print resolution and just spending bytes.

Quality is the JPEG compression level. JPEG is a lossy format — every level above zero throws away some data — but the difference between 90% and 60% quality is usually invisible on text and faces, and only barely visible on detailed photographs. The default is 60%, which is the sweet spot for documents (mostly text and simple graphics). Drop to 30-40% for aggressive compression on documents that don’t need to look great. Push to 80-90% for documents with photos that matter.

Think about it as: DPI sets the resolution, quality sets how much detail at that resolution gets preserved. Lower DPI saves a lot of space but blurs everything; lower quality saves space too but introduces compression artifacts.

The Real Trade-off (And Why We Say So)

Signegy’s compression rasterizes pages — it converts the PDF to a series of images and rebuilds the document from those images. This is the same technique most “easy” online compressors use because it works on any PDF and gives predictable results. The trade-off is that text in the output is no longer selectable text — it’s pixels of text inside a JPEG.

For most use cases this doesn’t matter. Email attachments, portal uploads, and printed documents work the same with or without selectable text. The recipient can read it, the printer can print it. The differences only show up if someone wants to copy a quote out of the PDF (they can’t), or search for a phrase inside it (they can’t), or use accessibility tools like a screen reader (less helpful).

If your document needs selectable text after compression — a contract you’ll search later, a long report a colleague will read, a legal filing — Signegy’s compression isn’t right for it. You want true PDF optimization (image stream re-encoding while preserving the underlying text and structure), which requires a different class of tool: Adobe Acrobat’s optimizer, Foxit’s PDF Compress, or the open-source qpdf and Ghostscript command-line tools.

Smallpdf and ilovepdf use rasterization on their free tiers too, but neither tells you. Their compressed files are also non-selectable.

When You Need This

The clearest case is email attachment limits. Gmail caps attachments at 25MB; Outlook at 20MB; many corporate email systems at 10MB. A scanned document or photo-heavy PDF often blows past these limits. Compression gets you under the cap with quality that’s visually fine for a one-time send.

Portal uploads are the second case. Tax authorities, mortgage applications, school portals, court e-filing systems — all have file size caps, often around 5-10MB, and rejecting uploads silently if you exceed. Compression solves it. Don’t push the quality too low for legal/official documents; the recipient may need to read fine print.

The third case is sharing. A PDF that’s small loads faster, downloads faster, and is easier to send via messaging apps. Even when there’s no hard limit, going from 30MB to 3MB for a quick share is just nicer for everyone.

Realistic Compression Ratios

For a calibration: a typical scanned document (image-only PDF at 200 DPI) compresses 60-80% at default Signegy settings. A photo-heavy travel itinerary or report compresses 40-70%. A born-digital document (created in Word, exported to PDF) with mostly text and vector graphics often only compresses 10-30% — and may not be worth running through the tool at all if the original is already under your target size.

If your input is under 1MB and mostly text, compression usually isn’t the right move; the file is already small. If your input is 20MB+ and image-heavy, compression often produces dramatic results.

Pair It With the Toolkit

The compress tool is often the last step in a longer workflow: merge several files, split the resulting document to share only the relevant pages, then compress to fit a portal’s upload limit. All in your browser, nothing uploads.

If you’re evaluating PDF tools more broadly, the Smallpdf alternative page compares Signegy’s compression directly to Smallpdf’s, including the limits Smallpdf doesn’t disclose. For the underlying privacy architecture, private PDF signing covers why browser-only processing matters.