Thank You for taking interest in GroupDocs.Conversion for Java and posting your query.
Let me answer your questions one by one.
Does Conversion Java support for HTML responsive output ?
You can use a responsive library like Bootstrap to make HTML output of GroupDocs.Conversion for Java 3.x responsive.
Support for image and css embed in HTML code ?
You can convert a document containing Images as HTML, about embedding CSS please tell me whether you are asking for a function in API, which will automatically add gvien CSS to HTML output ?
Can i edit the page border style of output html ?
Since Next Generation GroupDocs.Conversion for Java 3.x is a document conversion API and not an document editing API, you can not stylize the border through API, However you can stylize the border by adding your custom CSS in output HTML.
Does API support for PHP ?
Please elaborate this question, are you asking about converting a document in PHP format or you want to add PHP code in output HTML using the API ?
Moreover you may find following resources helpful
Please go through following resources and share your experience.
Keen to here from you.