How-To

How to Compress a PDF for Free: Reduce File Size Without Losing Quality

Sep 10, 2026 · 5 min read

Quick summary: To compress a PDF for free, use Preview on Mac (File → Export as PDF with Quartz Filter → Reduce File Size), Print to PDF on Windows, or Ghostscript on the command line with -dPDFSETTINGS=/ebook. Scanned PDFs typically shrink 70–90%; text-only PDFs 5–20%.

A PDF that is too large to email, upload, or share is one of the most common file frustrations. The good news: compressing a PDF almost never requires paid software. Whether you need to squeeze a 50 MB scan into a 2 MB attachment or just make a document load faster on mobile, the methods below cover every major platform — and our free AI PDF reader can help you read or summarize the result instantly after.

Why PDF files get so large

Most oversized PDFs fall into one of three categories:

Scanned documents — scanning at 300 DPI or above produces high-resolution image layers that bloat the file quickly.
Embedded fonts and graphics — design-heavy reports or presentations embed fonts, vector graphics, and high-res images at full quality.
Multiple versions of the same content — some PDFs accumulate revision history or duplicate embedded objects over many edits.

Understanding the cause tells you which compression method will have the most impact.

How to compress a PDF on any device

Method 1: Mac — Preview (built-in, free)

Preview can dramatically reduce PDF size using a built-in quartz filter:

Open the PDF in Preview (double-click or right-click → Open With → Preview).
Go to File → Export as PDF.
Click the Quartz Filter dropdown at the bottom of the save dialog.
Choose “Reduce File Size” and click Save.

Note: The Reduce File Size filter aggressively downsamples images. For scanned documents it works very well; for design-quality PDFs, test the output before sending.

For more control, a free alternative is to install PDF Squeezer (free tier) from the Mac App Store.

Method 2: Windows — Microsoft Print to PDF

Windows does not have a native PDF compressor, but you can re-export through the PDF printer:

Open the PDF in Microsoft Edge (built-in PDF viewer) or Adobe Acrobat Reader.
Press Ctrl + P to open the print dialog.
Select “Microsoft Print to PDF” as the printer.
Click Print and save the output.

This re-renders the document as a new PDF. It usually reduces size by 10–30%, depending on the original.

Method 3: Online — free, no install

Several browser-based compressors work without sign-up. Search for “compress PDF free” and choose any well-reviewed tool:

Upload your file.
Choose a compression level (most tools offer “Recommended”, “Strong”, or “Extreme”).
Download the compressed file.

Privacy note: Online tools send your file to a remote server. Do not use them for confidential, medical, or financial documents.

Method 4: iPhone and iPad — iOS Files app

iOS 16 and later can compress PDFs through the Shortcuts app, but the simplest method is:

Open the PDF in the Files app.
Long-press the file → Quick Look.
Tap the Share button and choose “Print”.
In the print preview, pinch outward on the preview thumbnail — this converts it to a PDF.
Tap the Share button again → “Save to Files”.

The resulting file is typically 30–50% lighter than the original.

Method 5: Command line — Ghostscript (Windows, Mac, Linux)

For batch processing or scripting, Ghostscript produces the smallest output:

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

The -dPDFSETTINGS flag controls quality:

Setting	Target use	Typical DPI
`/screen`	Screen display only	72
`/ebook`	Email, web, general reading	150
`/printer`	High-quality printing	300
`/prepress`	Professional print production	300+

/ebook is the best default for most documents — it produces a significant size reduction while keeping text sharp and images readable.

How to reduce PDF file size without losing quality

The key is targeting the right content type:

For scanned PDFs: downsampling images from 600 to 150–200 DPI is invisible to most readers and removes 60–80% of the file size.
For design files: use /printer in Ghostscript or “High quality” in online tools to avoid pixelated logos or blurry charts.
For text-only PDFs: compression rarely helps much. Instead, check whether embedded fonts can be subsetted — Adobe Acrobat’s “Optimize PDF” tool does this automatically.

How much can I compress a PDF?

Results vary widely:

Original type	Typical reduction
Scanned document (600 DPI)	70–90%
Photo-heavy presentation	40–70%
Mixed text and images	20–50%
Text-only document	5–20%

A 20 MB scanned contract can often shrink to under 2 MB with no visible difference on screen.

Common questions

Does compressing a PDF reduce text quality?

Text in PDFs is stored as vector data, not as pixels, so compression does not blur or degrade it. Only embedded images lose resolution when compressed.

Can I compress a password-protected PDF?

You need to remove the password first. See our guide on how to remove a password from a PDF, then compress the unlocked file.

Will compression remove my digital signatures?

Most standard compressors preserve digital signatures, but the “Print to PDF” method in both Windows and Mac destroys them because it re-renders the document as if printed. Check before using that method on signed contracts.

How do I make a PDF smaller to email?

Gmail, Outlook, and most email providers cap attachments at 25 MB. For attachments under that threshold, use the /ebook Ghostscript setting or the “Recommended” option in an online compressor — both stay well under the limit for typical documents.