Thanks very much Trevor for your response!
May be my question is silly but just wanted to be more clear.
We have created a custom uploader inside which we are using Kentico's Direct Uploader itself (~\CMSModules\Content\Controls\Attachments\DocumentAttachments\DirectUploader.ascx) and the extra thing which we included in this is a preview option of the file.
After this, we have a document type called "File Attachment" in which one of the field is "File" to which the above mentioned custom form control is assigned.
Now we've recently added a radio button list in the document type itself from Kentico UI which has three options:
Now, on the basis of selected file extension (before saving it to DB), we need to show/hide "Embed" option where I'm stuck. As per my understanding from various posts, we can assign the source to radio button list with some conditions as well using macro but before that I need to get the file extension.
Waiting for your help now!