If i want to allow user to upload only specific type of files, then how can i pu

Currently there is no property that valdiates file extension or type. You need to complete that task then check extension using script and valdiate.

We can use validations on the form only. You will only get the file extension after submitting the form so check the extension after the form node and get back to the form(Use chaining) again to show the validations if it fails.

when document is uploaded check the document extension using document function and get the extension if the desired extension is not there revert it else submit it.

okay thank you all