Yes this is possible:
In case of the uploaded file from a page you can save the 'Name' attribute of the 'file document' or specialization in the save microflow of the page.
If you create a document within Mendix you can also change the 'Name' attribute of the file document in the microflow in order to set the file name.
Hello Reshma,
I don't think you can change the value appearing in the control without using javascript or jQuery, however you can easily change the document name and format before download or on save.
In order to change a file's name and format you simply need to assign it in the Name attribute of your object (for example WeeklyReport.pdf)