破損したまたは読めないPDFファイルを修正する方法は？

Try opening the PDF in a different reader like Adobe Acrobat Reader, Chrome, or Foxit; 2. Use Adobe Acrobat Pro’s “Recover PDF” feature under File > Save As Other; 3. Repair via command line using qpdf with the command qpdf --repair --input-line-end-style=lf corrupted.pdf repaired.pdf; 4. Extract content using Google Drive by uploading and opening with Google Docs or use tools like PDF24 or Sejda; 5. Redownload the file from the original source after deleting the corrupted version; 6. Recover a previous version via Windows Properties, Mac Time Machine, or cloud backups; 7. Contact the sender to resend or re-export the file if corruption persists—starting with simple solutions often resolves minor corruption issues successfully.

If you're dealing with a corrupted or unreadable PDF file, don't panic—there are several methods you can try to recover or fix the file. Here’s a step-by-step guide to help you troubleshoot and potentially repair the PDF.

1. Try Opening the PDF in a Different PDF Reader

Sometimes the issue isn't with the file itself, but with the software you're using.

• Try opening the file in:
  • Adobe Acrobat Reader (most reliable)
  • Google Chrome or Microsoft Edge (both have built-in PDF viewers)
  • Foxit Reader, Sumatra PDF, or Preview (on Mac)
• If it opens in one of these but not in another, the problem is likely with your default PDF reader.

Tip: In Chrome, drag and drop the PDF into a browser tab, or go to chrome://settings/content/pdfDocuments and ensure "Download PDF files instead of automatically opening them" is turned off.

2. Use Adobe Acrobat’s Built-in Repair Tool

Adobe Acrobat Pro (not the free Reader) includes a repair feature.

• Open Adobe Acrobat Pro
• Go to File > Open and select the corrupted PDF
• If it fails, go to File > Save As Other > Recovered PDF
• Acrobat will attempt to extract as much content as possible

Note: This feature is only available in the full version of Acrobat, not the free Reader.

3. Repair Using Command Line (PDFtk)

PDFtk is a free tool that can sometimes repair broken PDFs.

• Download PDFtk (available for Windows, macOS, and Linux)
• Open command line and run:

  pdftk broken.pdf output repaired.pdf

• This reconstructs the PDF structure and may fix corruption issues

Note: PDFtk hasn’t been updated recently, so you may need to find a trusted mirror or use alternative tools like qpdf.

Alternative with qpdf (open-source and actively maintained):

qpdf --repair --input-line-end-style=lf corrupted.pdf repaired.pdf

4. Extract Text or Images from the Corrupted File

If the file won’t open fully, you might still be able to salvage content.

• Use Google Drive:
  • Upload the PDF to Google Drive
  • Right-click > Open with > Google Docs
  • It will convert the text (though formatting and images may be lost)
• Use online recovery tools like:
  • PDF24 Repair Tool (free, offline option)
  • Sejda PDF Repair
  • Smallpdf or iLovePDF (upload and repair online)

Caution: Be careful with sensitive documents when using online tools—uploaded files may be stored temporarily on their servers.

5. Check the File Source and Redownload

Corruption often happens during download or transfer.

• Delete the current file
• Redownload it from the original source
• Ensure your internet connection is stable during download
• Verify the file size matches the expected size

If transferring via USB or email, try sending it again—partial transfers can corrupt files.

6. Recover from a Backup or Previous Version

If you’ve opened the file before:

• On Windows: Right-click the file > Properties > Previous Versions
• On Mac: Right-click > Show in Finder > File > Revert To > Browse All Versions
• Check cloud backups (Google Drive, Dropbox, OneDrive) for older working versions

7. Contact the Sender or Source

If the file was sent to you or downloaded from a website, it might be corrupted at the source.

• Ask the sender to re-export or resend the PDF
• Request the original document format (e.g., Word, PowerPoint) and convert it again

Sometimes, if the file header or internal structure is severely damaged, full recovery may not be possible. But in many cases, especially with minor corruption, one of the above methods will get your content back.

Basically, start simple—try different readers and redownload—then move to repair tools if needed.

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