[SalesForce] ContentVersion FileExtension

As per docs :

http://www.salesforce.com/us/developer/docs/api/Content/sforce_api_objects_contentversion.htm The reason why the document was changed. This field can only be set when inserting a new version (revising) a document.

Refer this for revising an existing document if you did not get a chance to look at this : http://www.salesforce.com/docs/developer/cookbook/Content/revise_document.htm

Hope this helps.

        // Create a content version object  
        ContentVersion contentVersion = new ContentVersion();

        // Set the mandatory field pathOnClient  
        contentVersion.setPathOnClient(
                testUploadFile.getAbsolutePath());

        // Set the binary file data  
        contentVersion.setVersionData(readData);

        // Set the document ID of the document you wish to revise  
        contentVersion.setContentDocumentId(new ID("069x00000000C0j"));

        // Set the reason for change field on revision  
        contentVersion.setReasonForChange("Added total cost of"
                + "ownership graph");

        // You can add multiple versions if required by adding  
        // them to the array  
        SObject[] array = new SObject[] { contentVersion };
        SaveResult[] saveResultArray = binding.create(array);
        for (SaveResult sr : saveResultArray) {
            if (sr.isSuccess()) {
                System.out.println("created version with id:"
                        +  sr.getId());
            }
            else {
                System.out.println("Failed to create entity");
                for (Error error : sr.getErrors()) {
                    System.out.println(error.getMessage());
                }
            }
        }        

You have to populate FirstPublishLocationId, according to ContentVersion documentation:

ID of the location where the version was first published. If the version is first published into a user's personal library or My Files, the field will contain the ID of the user who owns the personal library or My Files. If the first version is published into a public library, the field will contain the ID of that library.

This field is only set the first time a version is published via the API. It isn't set when a version is published in Salesforce CRM Content or uploaded in Salesforce Files or. After the version is published, it is a read-only field.

If you don't set a FirstPublishLocationId via the API, this field defaults to the user's personal library, unless Origin is set to H, then this field defaults to My Files.

You can also reference Special Access Rules section from the link above where they have listed all requirements for the users trying to publish to public library.