On Windows 10 and 11 you may receive a .p7m file and see the "cannot open file" error. Windows doesn't recognize the signed format, but opening it is easy. Here's how to open a .p7m file on Windows.
Why Windows doesn't open .p7m files
The .p7m file is a digitally signed document (CAdES / PKCS#7). Windows doesn't have a default app for this signed envelope, so it shows an "unknown" file - it's not corrupt, you just need the right tool.
The easiest way: online, in your browser
You don't need to install anything or update Java. From Edge, Chrome, or Firefox on Windows:
1. Open the Open .p7m tool of P7M Viewer.
2. Drag the .p7m file onto the page.
3. View the document or download it in its original format.
It works the same on Windows 10 and Windows 11.
Save the document to PDF on Windows
After opening the file, to have it in PDF:
1. Press Ctrl + P (Print).
2. Choose "Microsoft Print to PDF" or "Save as PDF" as your printer.
3. Get a PDF ready to store or send.
Open multiple .p7m files on Windows
If you receive many, with multiple opening you upload all the .p7m files at once and download them extracted into a single ZIP archive.
Frequently asked questions
Do you need to install a program on Windows? No, the browser with P7M Viewer is enough.
Does this apply to both Windows 10 and 11? Yes, the online method is identical.
Is it free? Yes, opening a single file is free.
In summary
To open a .p7m file on Windows 10 or 11 you don't need software: upload it to P7M Viewer from your browser and view or download the document in a few seconds, for free.
