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PDFページをオンラインでクロップする方法 - 余白除去・空白トリミング

PDFページをクロップして不要な余白を除去し、空白をトリミングして文書をリサイズする方法を学びます。無料オンラインツールを使ったステップバイステップガイド。

公開日 2026年1月26日

Why Crop PDF Pages?

Cropping PDF pages is useful in many situations:

  • Remove excessive margins: Scanned documents often have large borders that waste space
  • Fix bad scans: Crop out shadows, edges, or artifacts from scanning
  • Resize for printing: Adjust page dimensions to fit specific paper sizes
  • Clean up screenshots: Remove unwanted areas from PDF screenshots
  • Prepare for binding: Adjust margins for professional printing and binding

Method 1: Using Online Crop Tool (Recommended)

The easiest way to crop PDFs is with our free Crop PDF tool:

  1. Upload your PDF: Drag and drop or click to select your file
  2. Set crop margins: Use the sliders to adjust how much to trim from each edge (top, right, bottom, left)
  3. Preview the result: The red overlay shows what will be cropped; the dashed border shows your final visible area
  4. Choose pages: Apply cropping to all pages or select specific ones
  5. Download: Click "Crop PDF" and download your cropped document

Understanding Crop Margins

Crop margins are measured as percentages of the page dimensions:

  • 5% crop: Removes a small border - good for slight cleanup
  • 10% crop: Moderate trimming - removes typical scan borders
  • 15-20% crop: Significant reduction - useful for removing large margins

You can set different values for each edge to handle asymmetric margins.

Quick Presets

Our tool offers several presets for common cropping needs:

  • Auto Crop (5%): Applies uniform 5% trimming from all edges
  • 10% All: Removes 10% from every edge
  • Wide Margins: Crops more from left/right (15%) than top/bottom (5%)

When to Crop vs. Remove Pages

Choose cropping when you want to:

  • Trim the edges of pages while keeping content
  • Remove whitespace around existing content
  • Resize the visible area uniformly

Choose removing pages when you want to:

  • Delete entire pages from the document
  • Extract only specific pages

Tips for Best Results

  1. Preview first: Always check the preview before cropping to ensure important content isn't cut off
  2. Keep original: Cropping is permanent - save a backup of your original PDF
  3. Combine with compression: After cropping, use Compress PDF to reduce file size further
  4. Check all pages: If pages have different content positions, you may need to crop them individually

What Happens When You Crop a PDF?

When you crop a PDF, the tool sets a "CropBox" that defines the visible area. The original content may still exist in the file but won't be visible when viewing or printing. For complete removal, some tools also update the MediaBox.

Note that cropping may not significantly reduce file size since the underlying content can remain. For file size reduction, always use a compression tool afterward.

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