A digital signature can be obtained from a certificate authority - a third party that issues them for use by other parties. A digital certificate provides the public key that can be used to validate the private key that is associated with a private key. It's possible to purchase a digital signature from a third party such as GloboSign or IdenTrust. '
However you can also obtain a digital signature through Windows. If you're running Windows 7 and Office 2016 look in Windows Explorer at C:\Program Files\Microsoft Office\root\Office16 for a file named SELFCERT.exe. Click on this file, and it will open a new dialog entitled, "Create Digital Certificate".
Enter a name for the digital certificate and then click OK. The next step is to open an MS Office and then go to the Developer tab. Click on Microsoft Security and then enable all macros. Click OK.
Then back on the Developer tab in the Code group click 'Visual Basic'. Go to the Tools menu and select Digital Signature.
Then click Choose and the digital signature should be automatically located. Be sure to save the MS Office file in a macros enabled format.
Then go to Start and simply type Internet Options. Click on the program called, 'Internet Options' which appears in the search results and in the new dialog click on the Contents tab and then click 'Certificates'.
You can then export your digital certificate for use elsewhere. The resulting file should have a 'cer' extension.