How Do You Compress a PDF? The Complete 2026 Guide for Every Platform

To compress a PDF, use an online tool like Adobe’s free compressor for instant results, Mac Preview for built-in offline compression (up to 86%), or Ghostscript for batch processing (up to 91%). The key is choosing the right method for your platform, privacy needs, and file type.

Why PDFs Are Large: Root Causes

A single full-page photo at 300 DPI adds 5–10 MB. Image data dominates most PDF file sizes.

DPI Settings and File Size

Technology Org confirms /ebook at 150 DPI is the sweet spot for screen viewing. Free PDF Compress notes text-only PDFs can achieve 70% reduction with zero visible loss.

4 Methods to Compress PDF on Any Platform

Method 1: Online Tools (No Installation)

Steps: Upload → select compression level (High/Medium/Low) → download.

Method 2: Mac Preview (Built-in, Offline)

1. Open PDF in Preview
2. File → Export
3. On macOS Sonoma or older: select “Reduce File Size” from Quartz Filter dropdown
4. On newer macOS: check “Optimize image for screen”
5. Click Save

Result: A 20-page scanned research paper at 45 MB drops to 8–12 MB. This is lossy — keep a backup of the original.

Method 3: Adobe Acrobat Pro (Windows, Paid)

1. Open Tools → Optimize PDF
2. Select file → click Reduce File Size
3. For granular control: File → Save as Other → Optimized PDF
4. Use PDF Optimizer to: downsample images, select compression algorithms (JPEG/JPEG2000/ZIP), subset fonts, strip metadata, flatten annotations
5. Click “Audit Space Usage” to see exactly what’s consuming space

Method 4: Ghostscript (Free, Cross-platform CLI)

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

Free PDF Compress reports scanned color PDFs reduced by 91% with minimal quality loss.

The “Print to PDF” Trap

PDF Candy tested the same document two ways:

Always use “Save as PDF” from within Word, Excel, or your source app. Never use “Print to PDF” as a compression method.

Decision Guide: Which Method to Use

Advanced: Content Streams and Font Subsetting

Content Streams

Neuxpower explains that “Print to PDF” stores text and images in large, opaque content streams that standard compressors cannot optimize. Fix: Go back to the source document and use “Save as PDF.” If the source is unavailable, re-print the PDF through a browser’s printer with “Save as PDF” as the destination.

Font Subsetting

Embedding only the characters actually used (not the entire font family) saves 400–600 KB per font. Enable subsetting in Acrobat’s PDF Optimizer or Ghostscript. This reduces file size by 5–15% with no impact on text quality.

Mobile Compression

Android

PDF Compressor: Resizer & Zip (SoulApps, updated April 2026) — free, works 100% offline. Supports compression levels (Best Quality / Balanced / Smallest Size), merging, splitting, and converting. No sign-in or watermark.

iOS

Adobe Fill & Sign includes PDF compression. Alternatively, use Lumin PDF (browser-based) with AES-256 encryption, SOC 2 Type 1, GDPR, and CCPA compliance. For maximum privacy, use an offline app.

Prevention: How to Avoid Large PDFs

Conclusion

Choose your compression method by platform: online tools for quick jobs, Mac Preview for offline Mac compression, Adobe Acrobat Pro for Windows with granular control, Ghostscript for batch automation. Always use “Save as PDF” instead of “Print to PDF” — the difference can be 34×. Start with 150 DPI (/ebook) for the best balance of size and quality.

FAQ

Will compressing a PDF affect its quality?

Reducing DPI and re-encoding JPEGs causes minor image quality loss, but text remains perfect. The “ebook” setting (150 DPI) produces no visible difference for screen viewing. Text-only PDFs achieve 70% reduction with zero quality loss.

Is it better to zip a PDF or compress it?

Compress the PDF directly. ZIP achieves only 5–10% reduction because PDFs are already internally compressed. Dedicated PDF tools achieve 50–90% by re-encoding images, subsetting fonts, and stripping metadata.

How to compress a password-protected PDF?

Most online tools cannot process locked PDFs. Remove the password first using Adobe Acrobat, compress the file, then re-add protection. Desktop tools like PDF24 or Acrobat Pro can compress locked files if you know the password.

What is font subsetting?

Font subsetting embeds only the characters actually used in the document instead of the entire font family. This saves 400–600 KB per font and reduces total file size by 5–15% with no visible impact.