Method that gets the specified custom data from the family. The custom data is returned if it exists or this method will fail if the specified custom data does not exist. You can use the HasCustomData property to determine if custom data exists.
| Name | Type | Description |
| ClientId | String | Input String that uniquely identifies the application that created the custom data. This is commonly the CLSID of the Add-In in a string form, e.g. "{C9A6C580-3817-11D0-BE4E-080036E87B02}", but it can be any string. |
| InternalName | String | Input String value that specifies the unique name of the custom data to retrieve. |
| CustomData | Byte | Output array of bytes containing the custom data. |