Fix: "Could not open the file because it is in an unknown format"
This error means the application trying to open your file does not recognise its internal structure — most commonly because .pub files are a proprietary Microsoft Publisher format that almost no software outside Publisher itself can read natively. Converting it to PDF first sidesteps the compatibility problem entirely.
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Converting…
About .pub to PDF conversion
What actually causes 'unknown format' when opening a .pub file?
Microsoft Publisher uses a binary format (.pub) that is not openly documented. Applications like LibreOffice, Adobe Acrobat, or macOS Preview have no built-in parser for it, so they report the file format as unknown rather than garbled output. The file is almost certainly not corrupted — the software just does not know how to read it.
Can OpenAny convert my .pub file so I can open it normally?
Yes. Upload your .pub file at OpenAny.io and it will be converted to PDF, which opens in any browser, PDF reader, or operating system without needing Publisher installed. The file is deleted from our servers within 60 seconds and no account is required.
What if I need to edit the content, not just view it?
A PDF conversion preserves the layout for viewing and printing but is not easily editable. If you need to edit the actual content, your best options are Microsoft Publisher itself, or uploading the .pub file to Microsoft 365 online (publisher.microsoft.com), which can open and re-export Publisher files directly.