To convert signatures on Microsoft .DOCM files one needs the "InkPicture" control from the Microsoft Tablet PC SDK for a signature.
In order to resolve your issue, please download the Microsoft Tablet PC SDK MSI installer.
Please download and install Microsoft Tablet PC SDK and try converting the document again.
ftp://ftp.blackice.com/Utils/MSTPCRT.msi
Please contact technical support for more details.