You need a folder level script to change the file name automatically.
You then can call the save function from a button in your form.
Script for Click:Event of a Save Button
event.target.mySaveDoc(event.target);
Folder level script
//Date function
function myDateString()
{
return util.printd("dd.mm.yyyy"+" - "+"HH.MM.ss", new Date());
}
//Save function
var mySaveDoc = app.trustedFunction(function(doc)
{
var aDocumentFileName = this.documentFileName;
if (aDocumentFileName == "MyForm.pdf")
{
app.beginPriv();
var myPath = app.getPath("user", "documents") + "/" + "MyForm" + " - " + myDateString() + ".pdf";
doc.saveAs(myPath);
app.endPriv();
}
}