The Open Action opens a file stored within the IFileData type property of the current object. A file is opened in an external application associated with the file's extension. The IFileData property that stores the file to be opened is specified via the FileAttachmentAttribute applied to the current persistent object declaration.
To ascertain why the Open Action is currently deactivated or disabled, use the DiagnosticInfo Action. If you need to change the Action's "active" or "enabled" state in code, use its ActionBase.Active or ActionBase.Enabled property, respectively.