WEB API TO CONVERT .DOCX AND .PDF TO .EPUB

We need a Web API that can automatically convert input documents in Word (.docx) or PDF (.pdf) format to professional-looking ebooks in EPUB (.epub) format. The input documents may contain only text or text and images.

IMPORTANT: A SIMPLE CONVERSION IS NOT ENOUGH
There are already several Third-Party software/packages that can perform a simple conversion from Word / PDF to EPUB. Such a conversion will just convert the Word / PDF file to an EPUB file with the usual changes such as reflowable content instead of page by the page content, minor changes in placement of text and images, and so on. This alone is not enough. Instead, the final EPUB document should look like a professionally designed ebook with an appropriate layout, margin, spacing, font, color, placement of text and images, and so on. The reason we say this is because our uploaders will be usually authors/writers who can write good content but may not be proficient in designing and formatting an ebook. So they may upload the input document with minimal or poor formatting. The software must not simply convert the input document to a corresponding EPUB document but must modify the layout, placement, etc. so that the final document will be a professionally designed ebook. The final document must be in standard .epub format that can be read on any of the popular EPUB readers available today. We hope we are clear with this part of the requirement.

DELIVERABLES
The project must be developed as an API that will accept a Word or PDF file as input and produce the EPUB file as output. The API must have secure authentication and authorization features to prevent public users from accessing it. There is no need for the programmer to develop any UI/UX design. The developer must set up the API in a web server (Windows or Linux – developer’s choice). The web server will be provided by us.
Final Deliverables:
The Solution / Project(s), including the entire source code
Setting up the API on a web server
Details of any third party software/packages used by the application
Documentation of the API calls and authentication and authorization scheme
Documentation/comments as required to clarify the source code and explain the working of the application

NOTE: Any third party software/packages used must be free for commercial use
PLATFORM: Windows or Linux – the developer can choose either platform.
LANGUAGE: The developer is free to choose any of the popular programming languages in use today.