Notes about the OCS file extension:
To open this file type, a required software must be installed. Without it you only see a Windows message "The following file cannot be opened
" (Windows 7) or "How do you want to open this file?
" (Windows 10) if you double-click the file. There click on "More apps"
and choose a suitable software to view such files on your PC or from email attachments.
The OCS file type is primarily associated with 'eDoc DigiSign' by Fujitsu Denmark. [Link is in Danish.] The .OCS file is a digital signature file formatted occording to the PKCS#7 standard. The document that is signed may be any kind, e.g., Word document, text file, or .EXE file.
Detailed information for file extension OCS:
Mime type: application/x-edocdigisign
To change file associations press Windows Key
and then Apps and Features
> Default apps
> Choose default apps by file type
Invalid file associations could be the result of underlying issues within your Windows PC.