How to Compress a PDF Online: Free, No Upload, No Quality Loss

A PDF that's too big to email, too slow to upload, or rejected by a form with a "max 10MB" limit is one of the most common file frustrations. The good news: most oversized PDFs are large because of embedded images — scanned pages or high-resolution photos — and compressing those images down to a sensible size can shrink the whole file by 50-90% with little to no visible difference on screen.

Compress a PDF in Your Browser (No Upload)

1. Go to convertlo.pro/compress-pdf.html
2. Drop in your PDF — Convertlo shows the original file size immediately
3. Pick a quality preset:
   • High: best quality, smaller file than the original but still sharp for print or zooming
   • Medium: balanced — the right choice for most email attachments and general sharing
   • Low: smallest possible file, best for quick previews or web uploads where quality matters less
4. Click Compress, check the new size and percentage reduction, then download

Under the hood, Convertlo renders each page of your PDF to an image at the chosen quality and rebuilds a new PDF from those images. This is especially effective for scanned documents and image-heavy files, where the original was often saved at far higher resolution than anyone will ever need on screen.

Why PDFs Get So Big in the First Place

Text and vector graphics are tiny — a 50-page text document might be under 1MB. The bloat almost always comes from images:

Reducing image resolution inside the PDF — which is exactly what the Low/Medium/High presets control — directly attacks the largest contributor to file size, which is why compression results in such dramatic reductions for scanned and image-heavy PDFs.

Will My PDF Still Have Selectable Text After Compression?

This depends on how the compressor works, and it's the single most important tradeoff to understand:

• Image-based compressors (including Convertlo's PDF Compressor) re-render every page as an image at the chosen quality. The result looks identical, file size drops dramatically, but the text is no longer selectable, searchable, or copy-pasteable — even if it was before.
• Content-stream compressors (typically desktop tools like Adobe Acrobat Pro or Ghostscript) re-compress the images and fonts already embedded in the PDF without converting pages to images. Selectable text stays selectable, but the size reduction is usually smaller than an image-based approach, especially for scanned PDFs that had no real text layer to begin with.

If your PDF is a scan (a photo of a paper document with no real text layer), image-based compression loses nothing you didn't already not have — the "text" was already just pixels. If your PDF is a digitally created document with real selectable text that you need to preserve (a contract, a report you'll search later), use a content-stream compressor instead, or run OCR first to add a text layer, then compress.

Compressing vs. Splitting a PDF

These solve different problems and are often combined:

• Compressing reduces the file size of the entire document while keeping every page — use this when the whole file needs to fit under a size limit (email attachments are commonly capped at 25MB on Gmail, 20MB on Outlook).
• Splitting divides a PDF into smaller files by page range, at full original quality — use this when you only need to send part of a larger document, like extracting one chapter from a 200-page report.

For a large document where only part of it is relevant, split out the pages you need first, then compress the smaller result if it's still too large. For a document where every page matters but the file is too big, compress directly.

How Much Can You Realistically Shrink a PDF?

Results vary enormously depending on what's inside the file:

• Scanned documents at 300-600 DPI: often 70-90% smaller after compressing to Medium or Low — a 40MB scan can become 5-8MB with no visible difference when reading on screen.
• Photo-heavy PDFs (portfolios, brochures, reports with embedded camera photos): 50-80% smaller is typical, since photos are usually embedded at much higher resolution than the page displays them.
• Text-only or mostly-vector PDFs (invoices, plain reports, exported spreadsheets): little to no reduction — these files are already close to their minimum size, and compression presets have nothing to act on.

If a PDF doesn't shrink much after compression, that's actually a good sign — it means the file wasn't bloated with oversized images to begin with.

Desktop Methods (No Upload Required)

Mac — Preview

Open the PDF in Preview, choose File → Export, and select the "Reduce File Size" Quartz filter from the dropdown. This applies a fixed compression level — less control than adjustable presets, but fast and entirely offline.

Windows / any OS — Ghostscript

Ghostscript is a free, scriptable PDF processor that can recompress embedded images to a target DPI without converting pages to images:

gswin64c -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

The /ebook setting targets roughly 150 DPI images, which is a good general-purpose balance. Other presets include /screen (smaller, ~72 DPI) and /printer (larger, ~300 DPI).

Frequently Asked Questions