Digital Signatures in XLSX Completed

Fully agree with Robert and voting for this feature.
Signing spreadsheet is actually mentioned in your current feature list so one would expect it would apply to more format than pdf...
This feature would be highly beneficial for all your components and the effort to implement should be reasonable as the process/method should be similar if not identical process for digitally signing all the main MS Office files. The email component would also greatly benefit from being able to read/write encrypted and signed emails.