create user interface SELECT FILE AND PAGE

var file1, firstPage, lastPage;

var w = new Window("dialog");
var g1 = w.add("group");
    g1.orientation = "row";
var b1 = g1.add("button", undefined, "File");
    b1.preferredSize.width = 75;
var et1 = g1.add("edittext", undefined, "");
    et1.preferredSize.width = 300;
    file1 = et1.text;
    b1.onClick = function () {
        file1 = File.openDialog("prompt");
        et1.text = file1.fullName;
    }
var g2 = w.add("group");
    g2.orientation = "row";
var st1 = g2.add("statictext", undefined, "");
    st1.preferredSize.width = 75;
var g3 = g2.add("group");
    g3.preferredSize.width = 200;
    g3.orientation = "column";
    g3.alignChildren = ["left", "center"];
var st2 = g3.add("statictext", undefined, "Page interval");
var g4 = g3.add("group");
    g4.orientation = "row";
var st3 = g4.add("statictext", undefined, "From:");
    st3.preferredSize.width = 30;
var et3 = g4.add("edittext", undefined, "1");
    et3.preferredSize.width = 50;
    firstPage = Number(et3.text);
    et3.onChange = function () {
        firstPage = Number(et3.text);
    }
var st4 = g4.add("statictext", undefined, "to:");
    st4.preferredSize.width = 15;
var et4 = g4.add("edittext", undefined, "1");
    et4.preferredSize.width = 50;
    lastPage = Number(et4.text);
    et4.onChange = function () {
        lastPage = Number(et4.text);
    }
var g6 = g2.add("group");
    g6.orientation = "column";
var b2 = g6.add("button", undefined,"OK");
    b2.preferredSize.width = 75;
var b3 = g6.add("button", undefined, "Cancel");
    b3.preferredSize.width = 75;
w.show();

var doc = app.activeDocument;
app.userInteractionLevel = UserInteractionLevel.DONTDISPLAYALERTS;
var pdfOptions = app.preferences.PDFFileOptions;

alert("File: " + file1 + "\nFrom: " + firstPage + "\nTo: " + lastPage);

// for (var i = firstPage; i < lastPage; i++) {
//     pdfOptions.pageToOpen = i;
//     var thisPlacedItem = doc.placedItems.add();
//     thisPlacedItem.file = file1;
// }