There is no specific "view file" service. You simply call the applicationManager open() method on a file and webOS will attempt to match the file with an application.
Example usage:
this.controller.serviceRequest(palm://com.palm.applicationManager', {
method: 'open',
parameters: {
target: "https:// crypto.stanford.edu/DRM2002/darknet5.doc"
},
onFailure: this.onFailureHandler
});