1)regarding file uploads if user wants to add a new extension then he could go through the following steps
default formats as: png, jpg, gif, pdf, rar, ppt, pptx, docx, doc, xls, xlsx, jpeg, csv, json

    1. Open the su and click on form field details.

    2. select the form in which you want to define the specific extension

   3 find field which have field type-file or if not, create a field create a field of fleld type file.

   4 mention the following sequence in default value of that field.

   SIZEINMB100 EXTPDF EXTXLS and so on.

2.How to hide upload button in any form 

 1 Need to add NOUPLOAD in default value of file field then it will hide upload button and show only file name .