Here is a list of all documented files with brief descriptions:

iothub.h	Global initialization and deinitialization routines for all IoT Hub client operations
iothub_client.h	Extends the IoTHubClient_LL with additional features
iothub_client_core_common.h	Shared enums, structures, and callback functions for IoT Hub client
iothub_client_ll.h	APIs that allow a user (usually a device) to communicate with an Azure IoT Hub
iothub_client_properties.h	APIs that serialize and deserialize properties modeled with DTDLv2
iothub_client_version.h	Functions for managing the client SDK version
iothub_device_client.h	Extends the IoTHubDeviceClient_LL with additional features
iothub_device_client_ll.h	APIs that allow a user (usually a device) to communicate with an Azure IoT Hub
iothub_message.h	The `IoTHub_Message` component encapsulates one message that can be transferred by an IoT hub client
iothub_module_client.h	Extends the IoTHubModuleClient_LL module with additional features
iothub_module_client_ll.h	APIs that allow a user to communicate with an Azure IoT Hub
prov_device_client.h	Extends the Prov_Device_LL module with additional features
prov_device_ll_client.h	Low level provisioning client