Adobe Acrobat PDF Compression – Guide and Free Alternatives

This page covers two audiences: (1) users who have Adobe Acrobat and want the exact steps to compress a PDF, including the difference between the Reduced Size PDF and PDF Optimizer methods, and (2) users who don’t have Acrobat Pro and need a free alternative. Includes Adobe Acrobat Online’s free tier limits and a comparison of the results from both Adobe compression methods.

H2-1: How to Compress PDF in Adobe Acrobat Pro

Method 1: Reduced Size PDF (Quick Method)

1. Open the PDF in Adobe Acrobat Pro (not Adobe Reader — Reader cannot compress)
2. Go to File → Save as Other → Reduced Size PDF…
3. In the compatibility dialog, select "Acrobat 10.0 and later" (most compatible, good compression)
4. Click OK
5. Choose a save location and filename — save as a new file to preserve the original
6. Click Save

What this method does: Applies standard compression to all images, removes redundant data, and downsamples images to approximately 150 DPI. Quick and suitable for most documents.

Typical result: A 10MB office document compresses to 2.5–4MB. A 20MB scanned document compresses to 4–8MB.

H2-2: Adobe Acrobat PDF Optimizer — Advanced Settings Explained

The PDF Optimizer gives full manual control over every compression parameter.

Access: File → Save as Other → Optimized PDF…

Key settings panels:

Images panel:

• Colour images: set to Bicubic Downsampling at 150 DPI for "standard"; 72 DPI for "extreme"
• Greyscale images: same as colour
• Monochrome images (black/white scans): set to 300 DPI (monochrome compresses better at higher DPI using CCITT Group 4 compression)
• Compression type: JPEG for photos (lossy), ZIP for diagrams/charts (lossless)
• Image quality: Medium (40–60% JPEG quality) for size priority; High (80%) for quality priority

Fonts panel:

• Subset embedded fonts when percent of characters is below: 100% (always subset)
• Unembed fonts: select standard fonts (Arial, Times New Roman, Helvetica) that are available on all systems

Discard Objects panel (important for size reduction):

• Discard all comments and form fields: useful for finalised documents
• Discard all JavaScript: removes scripts embedded in PDFs
• Discard embedded page thumbnails: thumbnail previews add 10–50KB per page
• Discard document tags: removes accessibility tags (use with caution — removes screen reader support)

Discard User Data panel:

• Remove all hidden layers
• Remove embedded search index
• Remove private data of other applications

Typical result with full optimisation: A 10MB scanned document achieves 1.5–3MB at medium image quality, significantly outperforming the Reduced Size PDF method.

H2-3: Adobe Acrobat Online — Free Tier Limits

Adobe offers a web-based PDF compressor at acrobat.adobe.com that does not require Acrobat Pro installed.

Key limitation: Adobe Acrobat Online applies a fixed compression algorithm with no user control over DPI or quality settings. The Reduced Size PDF in the desktop Acrobat Pro offers the same one-click simplicity with better compression results.

H2-4: Free Alternatives If You Don’t Have Acrobat Pro

For users who need Adobe Acrobat Pro’s output quality without the subscription: Ghostscript is the closest free equivalent. The command: `` ghostscript -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook \ -dCompatibilityLevel=1.4 -dBATCH -dNOPAUSE \ -sOutputFile=output.pdf input.pdf ` /ebook = 150 DPI (equivalent to Acrobat’s Reduced Size PDF), /screen` = 72 DPI (equivalent to Acrobat’s extreme settings).

Frequently Asked Questions