Manatee

Preview can't open this PDF: causes and fixes

· 6 min read

When Preview says it can’t open a PDF, the file is one of four things: not actually a PDF (a web page or error message saved with a .pdf name), an incomplete download or cloud placeholder, a PDF with a password or a feature Preview does not render, or a PDF that is genuinely damaged. The first three take a minute to check and fix. The fourth needs a repair, and that can be done on the Mac without sending the file anywhere.

Cause 1: it is not a PDF

This is the most common cause, and the most overlooked. Websites and email systems frequently hand you an HTML error page, a login prompt, or a “this link has expired” message and save it with the filename you expected.

How to check:

  1. Look at the size in Finder (Command-I). A 40-page report is not 3 KB.
  2. Open Terminal and run file /path/to/document.pdf. The output says “PDF document” for a real one, or “HTML document”, “Zip archive”, “Microsoft Word”, or similar for an imposter.
  3. Alternatively, open the file in TextEdit. A PDF starts with %PDF-. A web page starts with <html or a doctype declaration.

The fix is to go back to the source and download again, preferably while logged in. If the file turns out to be a Word or ZIP file, rename the extension and open it with the right app.

Cause 2: the download never finished

Cloud services and browsers both produce files that look present but are not.

  • Cloud placeholders. iCloud Drive and other sync services show files that live only in the cloud with a cloud icon. Double-clicking should start the download, but Preview sometimes opens the placeholder before the data arrives. Right-click the file, choose Download Now, wait for the icon to clear, and try again.
  • Partial downloads. A browser download that failed partway may leave a file with the right name and the wrong size. Check the size against the original, and re-download.
  • Email attachments on a slow connection. Mail can show an attachment icon before the whole message is fetched. Open the message, wait, and drag the attachment to the Desktop once it has a proper size.

In all of these, the cure is the same: get the complete file. Repairing a partial download will, at best, return the pages that arrived.

Cause 3: a password or a feature Preview cannot handle

A few PDF types open fine elsewhere and fail in Preview, or open in Preview with blank pages.

  • Encrypted PDFs. Preview does ask for a password when it recognizes encryption, but a PDF with an unusual security handler can fail outright. Try a browser. If the file needs a password you do not have, no repair tool will remove it, and Manatee does not attempt to.
  • XFA forms. Some government and corporate forms use an XML form layer that only specific readers support. Preview shows a page saying the document requires a different viewer, or shows nothing. These are not damaged; open them in a reader that supports XFA.
  • PDF portfolios and attachments. A PDF that is really a bundle of other files shows a cover page or nothing in Preview. The contents are accessible in a full-featured reader.
  • Very large or very complex files. Preview can stall on enormous scans or maps. Give it time, or try Quick Look (select the file and press the space bar), which sometimes succeeds where Preview hangs.

Cause 4: the file is damaged

If the file is the right size, file identifies it as a PDF, it is not encrypted, and it still fails in Preview, Quick Look, and a browser, the file is corrupted. The usual damage is to the cross-reference table at the end, which readers need as their entry point, and it happens when a save or transfer stopped early.

Check the ending in Terminal: tail -c 32 /path/to/document.pdf. A complete PDF ends with %%EOF. Anything else means it was truncated.

The fix is a repair that scans for the page objects that survive and rebuilds the table. The Repair mode in Manatee does this on the Mac:

  1. Open Manatee (the first 24 hours are free with every feature, no card or email).
  2. Drop the PDF in, or right-click it in Finder and choose Fix with Manatee.
  3. Wait for the job, then read the outcome: Fixed, Partial (with an exact count such as 34 of 41 pages), or Not fixable.
  4. Open the repaired copy next to the original. The original is never modified.

Pages that were never in the file cannot be recovered; a Partial result is the honest maximum. How to repair a corrupted PDF on a Mac goes deeper on what repair can and cannot do, and Partial recovery explained explains how to read the outcome.

A quick decision list

  1. Is the size plausible? If not, re-download or find the original.
  2. Does file say it is a PDF? If not, rename or re-download.
  3. Does it have a cloud icon or a partial-download name? Wait for it or fetch it again.
  4. Does a browser open it? If yes, Preview lacks a feature; use the browser or export a fresh copy from it.
  5. Does it end in %%EOF? If not, it is truncated; repair it.
  6. Nothing above applies? Repair it, and if the result is Not fixable, the content was never in the file.

Questions

Preview opens the PDF but every page is blank. Is it damaged? Possibly, or it may be an XFA form, or the page content relies on a font or image that failed to load. Try a browser first. If it is blank everywhere, a repair can sometimes reconnect the page content; if it works in a browser, export a new PDF from there.

The PDF opens on my iPhone but not on my Mac. Why? The iPhone may have the complete file while the Mac has a cloud placeholder or an older partial copy. Compare sizes. AirDropping the file from the phone to the Mac gets you the complete version.

Can I fix a PDF by changing the extension? Only if the extension is wrong in the first place (a Word file or a ZIP named .pdf). Renaming a damaged PDF does nothing; the structure inside is what matters.

Does repairing the PDF send it anywhere? Not with Manatee. The repair runs on the Mac, with no upload and no account. For documents you would not want in a third party’s hands, that is the reason to avoid web-based PDF fixers.