Hi
I can develop your project in C++, or C#. This will depend on the availability of a library for sign the document in PDF, DOC(or DOCX) format. In C++ the executable will not need another dependencies, and can be executed on any windows version (from Windows 7, if you need to run it from another, older Windows version, please tell me). In C# I can develop the tool more faster, but it maybe need the .NET framework installed on the PC you work on.
Any way, I offer also proper validation of the arguments passed trough the command line, with correct and meaningful displayed error messages.
I hope to be the selected freelancer.
Warm Regards.