#target illustrator

var artboardIndex = 1;
var artboards = app.activeDocument.artboards;
var destFolder = Folder.selectDialog("Select the destination folder");
var destFileName = app.activeDocument.name;
var docWidth = prompt("Enter the new document width (in inches):") * 72;
var docHeight = prompt("Enter the new document height (in inches):")* 72;

// select the objects on the artboard
artboards.setActiveArtboardIndex(artboardIndex);
app.activeDocument.selectObjectsOnActiveArtboard();

// calculate the scale factor based on the original artboard size
var currentArtboard = app.activeDocument.artboards[artboardIndex];
var currentArtboardBounds = currentArtboard.artboardRect;
var pastedObjectsWidth = currentArtboardBounds[2] - currentArtboardBounds[0];
var pastedObjectsHeight = currentArtboardBounds[1] - currentArtboardBounds[3];
var scaleFactor = Math.min(docWidth / pastedObjectsWidth, docHeight / pastedObjectsHeight);

// copy and paste
app.copy();
var newDoc = app.documents.add(DocumentColorSpace.CMYK, docWidth, docHeight);
var ABR = newDoc.artboards[0].artboardRect = [0, 0, docWidth, -docHeight];
app.paste();
newDoc.views[0].centerPoint = [docWidth / 2, -docHeight / 2];

// group, re-size and re-position
app.executeMenuCommand("group")
var pastedObjects = newDoc.selection[0];
pastedObjects.width *= scaleFactor;
pastedObjects.height *= scaleFactor;
pastedObjects.position = [docWidth / 2 - pastedObjects.width / 2, -docHeight / 2 + pastedObjects.height / 2];
var newFile = new File(destFolder + "/" + destFileName);
app.executeMenuCommand("ungroup");

newDoc.saveAs(newFile);
newDoc.close();