What Is a P7S or P7M File?

P7S, P7M and CMS files

The files with the extension .p7s, .p7m or .cms contain a PKCS#7 / CMS signature (RFC 5652), and the CAdES signatures (ETSI EN 319 122-1) that the eIDAS Regulation (EU) No 910/2014 uses for advanced and qualified electronic signatures are stored in the same kind of file. They can be opened by any software that reads these standards.

By default the signed file contains the document and its signature. The signature can also be saved in a separate file (detached signature), and the original file is not changed: a detached signature contains only the signature, and it is checked together with the signed file next to it (for example invoice.pdf for invoice.pdf.p7s).

What is the difference between P7S and P7M?

Both extensions contain a PKCS#7 / CMS signature in the same format. The extension you choose depends on the system that receives the file.

How to open a P7S or P7M file

1. Download and install P7S P7M Viewer (free 30-day trial).
2. Open the .p7s, .p7m or .cms file in the program. It checks the signature on your computer and shows the signer, the signing date, the signature format and whether the signature is valid.
3. Click Open unsigned file to open a copy of the signed document, without the signature, in the program associated with its type, or Save unsigned file to save the copy. This is the way to read, for example, an XML invoice or a PDF contract that you received as a .p7m file.

What the signature tells you

• the signer and the issuer of the certificate
• the signature format (for example CAdES-B-B, CAdES-B-T, CAdES-B-LT, CAdES-B-LTA, CMS)
• the signing date, and whether it is declared by the signer or certified by a time stamp
• the certificate status (valid, expired, not valid yet)
• the signature integrity: valid, or not valid if the file was changed after signing

To find out whether a signature is a qualified electronic signature (qualified certificate, QSCD), validate the file with the validation tool of the European Commission (DSS – eSignature validation) or with another eIDAS-compliant validator.

How to create a P7S or P7M file

P7S Signer digitally signs files of any type (PDF, Word, images, XML, archives) with X.509 certificates. It creates CAdES signatures (ETSI EN 319 122-1, baseline levels B-B, B-T, B-LT and B-LTA) and PKCS#7 / CMS signatures, saved in P7S, P7M or CMS files. You can sign a single file or a complete folder of files in one operation.

Before you start, check the signature format and the file extension required by the receiving system (for example CAdES-B-B or CAdES-B-LT, P7M or P7S), and choose the same options in P7S Signer.

Frequently asked questions