Cross-Platform Productivity App Development

I'm looking for an experienced developer to create a native productivity app for both Android and iOS.

Key features include:
- Document sharing capabilities
- Syncing with a host server
- User authentication via username/email and password

Ideal candidates will have:
- Proven experience in developing native mobile applications for both Android and iOS
- Strong background in server synchronization and document sharing functionalities
- Expertise in implementing secure user authentication methods

Please provide examples of similar work and a timeline for project completion.