From ReactOS

Windows Clipboard Object

typedef struct _CLIPDATA
{
   HEAD  head;
   DWORD cbSize;       // Size of clipboard data.
   BYTE  bClipData[0]; // Data from clipboard.
} CLIPDATA, *PCLIPDATA;

References

• Based what we know from NtUserConvertMemHandle(PVOID pClipData, SIZE_T cdSize)