How to Compress a PDF File (5 Free Methods to Reduce Size)

Need to shrink a PDF that's too large to email or upload? You're not alone - it's one of the most common PDF problems.

The good news: you can usually reduce PDF file size by 50-90% without noticeable quality loss. And you don't need paid software to do it.

In this guide, I'll show you 5 free methods to compress PDF files, from quick online tools to advanced techniques for maximum compression.

Why Are Some PDFs So Large?

Before we compress, it helps to understand why PDFs get bloated:

• High-resolution images - Photos and graphics are the #1 cause of large PDFs
• Embedded fonts - Each font adds to file size
• Unoptimized scans - Scanned documents often have unnecessary resolution
• Multiple layers - Design files may have hidden layers
• Metadata - Hidden data like edit history adds size

Knowing this helps you choose the right compression level.

When Do You Need to Compress a PDF?

Common situations where smaller PDFs help:

• Email attachments - Most email providers limit attachments to 25MB
• Website uploads - Job applications, forms, and portals have size limits
• Cloud storage - Smaller files save storage costs
• Faster sharing - Compressed PDFs download faster when shared via links
• Mobile viewing - Smaller files load faster on phones

Let's look at the solutions.

Method 1: Compress PDF Online (Quickest)

Best for: Fast compression without installing anything

The fastest way to shrink a PDF is with a free online tool. Here's how with Edesy's PDF compressor:

Step-by-Step:

1. Go to edesy.in/tools/compress-pdf
2. Upload your PDF by clicking the upload area or dragging your file
3. Choose compression level:
   • Low - Best quality, modest size reduction (10-30%)
   • Medium - Balanced quality and size (30-60%)
   • High - Maximum compression, some quality loss (50-90%)
4. Click "Compress PDF" and download the smaller file

Why this method is secure: Your PDF is processed entirely in your browser. Files never leave your device or get uploaded to any server.

Pros:

• Works on any device (computer, phone, tablet)
• 100% private - no upload to servers
• Free with no signup
• Shows exact size reduction

Cons:

• Requires internet connection
• Very large files (100MB+) may be slow

Method 2: Using Preview on Mac

Best for: Mac users who want a built-in solution

Preview has a "Reduce File Size" option that works well for basic compression.

Step-by-Step:

1. Open your PDF in Preview
2. Go to File > Export
3. Click the "Quartz Filter" dropdown
4. Select "Reduce File Size"
5. Save the compressed file

Pros:

• Built into macOS
• Quick and easy
• Works offline

Cons:

• Mac only
• Can over-compress images (low quality)
• No control over compression level

Pro tip: If Preview compresses too aggressively, use an online tool for more control.

Method 3: Using Adobe Acrobat Online (Free Tier)

Best for: Users who want Adobe's compression engine

Adobe offers a free online PDF compressor (with limits).

Step-by-Step:

1. Go to adobe.com/acrobat/online/compress-pdf.html
2. Upload your PDF
3. Choose compression level (High, Medium, Low)
4. Download the compressed file

Pros:

• Adobe's reliable compression
• Three quality options

Cons:

• Requires Adobe account
• Limited free compressions per day
• Files are uploaded to Adobe's servers

Method 4: Compress PDF on Mobile

Best for: Compressing PDFs from your phone

Several mobile apps offer PDF compression.

iOS Options:

• PDF Expert - Free compression feature
• Shortcuts app - Create a compression automation
• Files app - Some compression when using "Create PDF"

Android Options:

• iLovePDF - Free mobile app
• PDF Compressor - Simple and free
• Adobe Scan - Compresses scanned docs

Pros:

• Compress on the go
• Good for quick fixes

Cons:

• May have ads in free versions
• Less control over compression settings

Method 5: Using Python (For Developers/Power Users)

Best for: Batch compression or automation

For compressing many PDFs or integrating into workflows, Python is powerful.

Prerequisites:

pip install PyPDF2 Pillow pdf2image

Basic Compression Script:

from PyPDF2 import PdfReader, PdfWriter
 
def compress_pdf(input_path, output_path):
    """
    Basic PDF compression by removing unnecessary data.
    """
    reader = PdfReader(input_path)
    writer = PdfWriter()
 
    for page in reader.pages:
        page.compress_content_streams()  # Compress page content
        writer.add_page(page)
 
    # Remove unnecessary metadata
    writer.add_metadata({})
 
    with open(output_path, 'wb') as output_file:
        writer.write(output_file)
 
    # Report size difference
    import os
    original_size = os.path.getsize(input_path)
    compressed_size = os.path.getsize(output_path)
    reduction = (1 - compressed_size / original_size) * 100
 
    print(f"Original: {original_size / 1024:.1f} KB")
    print(f"Compressed: {compressed_size / 1024:.1f} KB")
    print(f"Reduction: {reduction:.1f}%")
 
# Usage
compress_pdf("large_document.pdf", "compressed_document.pdf")

Advanced: Image-Heavy PDF Compression

For PDFs with lots of images, you need to recompress the images:

import subprocess
import os
 
def compress_with_ghostscript(input_path, output_path, quality="ebook"):
    """
    Use Ghostscript for aggressive compression.
 
    Quality options:
    - screen: lowest quality, smallest size (72 dpi)
    - ebook: medium quality (150 dpi)
    - printer: high quality (300 dpi)
    - prepress: highest quality, largest size
    """
    gs_command = [
        "gs",
        "-sDEVICE=pdfwrite",
        "-dCompatibilityLevel=1.4",
        f"-dPDFSETTINGS=/{quality}",
        "-dNOPAUSE",
        "-dQUIET",
        "-dBATCH",
        f"-sOutputFile={output_path}",
        input_path
    ]
 
    subprocess.run(gs_command, check=True)
 
    # Report results
    original = os.path.getsize(input_path) / 1024
    compressed = os.path.getsize(output_path) / 1024
    print(f"Compressed from {original:.0f}KB to {compressed:.0f}KB")
 
# Requires Ghostscript installed: brew install ghostscript (Mac) or apt install ghostscript (Linux)
compress_with_ghostscript("large.pdf", "small.pdf", "ebook")

Pros:

• Batch process hundreds of files
• Integrate into automated workflows
• Maximum control over compression

Cons:

• Requires technical knowledge
• Overkill for occasional compression

Which Method Should You Use?

Tips for Better PDF Compression

1. Start with Medium compression - You can always compress more if needed
2. Check quality after - Open the compressed PDF and zoom into images
3. Compress before merging - Compress individual files, then merge
4. Remove unnecessary pages - Delete blank or unneeded pages first
5. Use the right tool for the job - Image-heavy PDFs need aggressive compression; text PDFs are already small

How Much Can You Reduce File Size?

Typical results by PDF type:

Common Questions About PDF Compression

Will compressing reduce quality?

It depends on the compression level. Low compression maintains near-original quality. High compression may reduce image clarity but keeps text sharp.

Why didn't my PDF get much smaller?

If your PDF is mostly text or already compressed, there's less to reduce. Try a higher compression level or check if images are already low resolution.

Can I compress a password-protected PDF?

You'll need to unlock it first. Use an Unlock PDF tool, then compress.

How do I compress a PDF for email?

Most email limits are 25MB. Use medium or high compression to get under that limit. For very large files, consider splitting into multiple PDFs.

Wrapping Up

Compressing PDFs is straightforward with the right tool. For most people, a free online compressor that processes locally is the fastest and most secure option.

Mac users can use Preview for basic compression, and power users can automate the process with Python or Ghostscript.

Remember: start with medium compression and only go higher if you need more size reduction.

Related Tools:

• Compress PDF Online - Free, no signup
• Merge PDF - Combine multiple PDFs
• Split PDF - Separate into smaller files
• PDF to JPG - Convert to images