How to Compress a PDF in Adobe Acrobat

PDFs get large from embedded images, fonts, and scanned pages. Adobe Acrobat has two ways to shrink them: Reduce File Size (a quick preset in both Pro and Standard) andOptimize PDF (full control, Pro only). This guide walks through both in Acrobat DC 2024 and later, explains what each quality preset actually does, and shows a free, local alternative in IXPDF that needs no install.

Two ways to compress in Acrobat

Acrobat exposes compression through two different tools with different audiences:

• File → Reduce File Size: a one-click preset dialog with three quality levels. Available in both Pro and Standard. Best for most users — pick a preset, save, done.
• Tools → Optimize PDF: a full optimization panel with control over image downsampling, compression, font subsetting, and object streams. Pro only. Best when the presets do not give the size/quality balance you need.

Method 1: Reduce File Size (quick, both editions)

1. Open your PDF in Adobe Acrobat (Pro or Standard).
2. Go to File → Reduce File Size (in some versions under File → Save As Other → Reduced Size PDF).
3. A dialog asks for compatibility and quality. Pick:
   • Medium quality (150 dpi): the default. Balances size and readability. Good for email and screen reading. Images are downsampled to 150 dpi.
   • High quality (300 dpi): keeps images at print resolution. Larger file, but prints cleanly. Use for documents that will be printed.
   • Low quality (72 dpi): aggressive. Images downsampled to screen resolution. Smallest file, but images look soft. Use only for preview thumbnails or when size is the only thing that matters.
4. Pick Retain Existing for compatibility (keeps the PDF version) or choose a specific Acrobat version if you need backward compatibility.
5. Click OK and save the compressed PDF. Compare it side by side with the original before relying on it.

Method 2: Optimize PDF (full control, Pro only)

1. Open your PDF in Adobe Acrobat Pro.
2. Go to Tools → Optimize PDF. The Optimize panel opens on the right.
3. Click Advanced Optimization. The PDF Optimizer dialog appears with six tabs: Images, Fonts, Transparency, Clean Up, Discard Objects, and User Data.
4. Images tab: the most important one. SetDownsample to Bicubic and pick a target DPI for color, grayscale, and monochrome images separately. Anything above the target is downsampled; below is left alone. SetCompression to Automatic (JPEG) for photos or ZIP for flat-color graphics.
5. Fonts tab: check Embed All Fonts if you want portability, or Subset Embedded Fonts to include only the glyphs actually used (smaller file).
6. Clean Up tab: check Optimize the PDF for Fast Web View (reorders objects for progressive download) andFlatten Form Fields if you do not need editable fields.
7. Discard Objects tab: selectively drop bookmarks, thumbnails, embedded print streams, or hidden layers. Each one shrinks the file.
8. Click OK and save. The PDF Optimizer reports the before/after size so you can see the gain.

You can save your Advanced Optimization settings as a profile and reuse it — useful if you compress many PDFs with the same settings.

What each quality preset does to your PDF

Fonts are subset in all three presets. Text stays crisp — only images are affected by the DPI change.

Common mistakes

• Using Low quality for a printable document. 72 dpi images look fine on screen but pixelated on paper. Use Medium or High for anything that will be printed.
• Compressing a compressed PDF. Each pass degrades images further. Compress once at the right preset; do not re-compress.
• Forgetting to compare. Always open the compressed PDF and check the images and text. If a chart is now unreadable, redo at a higher quality.
• Compressing a scanned PDF with Reduce File Size.Scanned pages are images — Reduce File Size will downsample them, which can make text blurry. For scanned PDFs, consider re-OCR at the target resolution instead.