Why does Preview say a PDF is damaged when it opens in another app?

Preview uses its own PDF engine. If the file has minor structural issues, Preview may reject it while another viewer, such as Adobe Acrobat Reader, can still open it. The file might have a wrong header or a missing end-of-file marker.

Can I repair a PDF with a missing header?

Possibly. If the header is missing but the rest of the file is intact, some repair tools can rebuild the header. However, if the trailer is also missing, the file is likely truncated and may not be recoverable without a dedicated service.

What should I do if the PDF is a placeholder in iCloud?

Double-click the file in Finder to force a download, or right-click and choose 'Download Now'. After the download completes, the file should open in Preview. If it still fails, move it out of iCloud and try again.

Is there a way to prevent this error in the future?

Always check that downloads finish completely before opening. For files received by email, save them to disk first. Avoid renaming files from other formats to .pdf. If you use iCloud, make sure files are downloaded before you try to open them.

PDF Won't Open on Mac: Preview "Could Not Be Opened" Fixes

You double-click a PDF and Preview throws this: The file "name.pdf" could not be opened. It may be damaged or use a file format that Preview doesn't recognize. The file looks like a PDF. It has the right extension. But Preview cannot parse its internal structure. The cause is a truncated download, a file that is actually an HTML page or a ZIP archive wearing a .pdf extension, or a PDF that has been corrupted. Start with Terminal commands to inspect the file, then move to repair and recovery.

What the Preview Error Really Means

Preview reads the beginning of the file and expects a valid PDF header. If it cannot find one, you get the error. The same thing happens when it reaches the end and the expected end-of-file marker is missing. The file might be a placeholder. It might be a completely different file type that someone renamed.

Confirm the file is actually a PDF before you attempt any repair. Check its size and location. A file that is only a few kilobytes and arrived via download is often an error page saved as .pdf. A file in iCloud Drive might not be downloaded yet. The sections below give you exact commands and steps to check these possibilities.

Check the PDF Header and Trailer in Terminal

Terminal gives you a quick, reliable way to see if the file is a real PDF. Open Terminal (in /Applications/Utilities/). Drag the file into the Terminal window after typing a command, or navigate to its folder.

Three commands that reveal the truth

Type head -c 8 /path/to/file.pdf and press Return. The output must be exactly %PDF- followed by a version number such as 1.7. Anything else means the file is not a valid PDF.
Type tail -c 32 /path/to/file.pdf and press Return. The last characters should include %%EOF. If you do not see that, the file is truncated or corrupted.
Type file /path/to/file.pdf. The output tells you the real type: PDF document, HTML document, or Zip archive. This catches renamed files instantly.

If the header or trailer is wrong, the file is damaged. Try opening it in another viewer or use a repair tool (see the final section).

Check for ICloud Placeholders

A PDF stored in iCloud Drive with Optimize Mac Storage turned on may exist on your disk only as a small placeholder. Preview sees the placeholder, tries to open it, and fails. The actual data is not local.

Force a download

In Finder, go to iCloud Drive and locate the PDF. A small cloud icon next to the filename means the file is not fully downloaded. Double-click the file to download it, or right-click and choose Download Now. Wait for a large file to finish. Then try opening it again in Preview.

If the file still will not open, move it to your Desktop or Documents folder, outside iCloud, and try again. This rules out any iCloud sync issue.

Test in a Second PDF Viewer

Preview is not the only PDF reader on your Mac. Adobe Acrobat Reader is free for macOS and uses a different PDF engine. If Preview fails, Acrobat Reader might open the file. It might also give you a more specific error that points to the actual problem.

Download and install Adobe Acrobat Reader, then open your PDF with it. If it opens, use Acrobat to repair the file by saving a copy (File > Save As, then choose PDF). If Acrobat also fails, the file is too damaged for either viewer to read directly.

Password-protected and DRM-locked files

PDFs protected with an open password prompt for it in Preview. Enter the password and the file opens. Certificate-encrypted or DRM-protected PDFs may only open in Adobe software. If you see a prompt for a certificate or a message about permissions, open the file in Acrobat Reader.

Repair a PDF by Exporting from Preview

If the file opens but some pages are blank, or if Preview displays the error only for certain pages, export a new copy. This rewrites the PDF structure and drops damaged objects.

Open the PDF in Preview. Go to File > Export as PDF.
Choose a new filename and location, then click Save.
Open the new file. If it opens correctly, you have a repaired copy. If it still fails, the original file is too corrupt for this method.

This does not fix a completely unreadable file. Try it anyway. It is quick and uses only built-in tools.

Use a Dedicated PDF Repair Service

If the checks above do not work, the PDF file may be severely damaged. A dedicated repair service can recover the content from a corrupted file. One option is repairpdffile.net, which repairs PDF files online. You upload your file and receive a repaired version. This is a last resort after you have confirmed the file is not a placeholder, not a renamed file, and not a simple header or trailer issue.

Before using any online service, make sure the file does not contain sensitive information you would not want to share. If it does, try the Terminal checks and Preview export first.