Cross-Platform Document Signing App Development

I need a mobile app for both Android and iOS that enables me to sign documents, send them via email for clients' signature, and mark documents with my own signatures.

Key Features:
- The ability to sign documents and send them via email for clients' signature
- Option to add my own marks/signatures to documents
- Support for Any file type
- Both cloud and local storage for documents

Security:
- The app should utilize Email verification to ensure the security of the signing process.

Ideal Skills and Experience:
- Proficiency in Android and iOS app development
- Experience in developing secure document management systems
- Familiarity with cloud and local storage integration
- Strong understanding of email verification implementation
- Prior work on cross-platform app development would be advantageous

Please note that I'm open to discussing additional features or suggestions that could enhance the app's functionality.