var pref = app.preferences.PDFFileOptions;
pref.pageToOpen = 2; //set page number you want to place.
pref.pDFCropToBox = PDFBoxType.PDFMEDIABOX;
var pdfOptions = app.preferences.PDFFileOptions;
var obj = app.activeDocument.layers[0].placedItems.add();
var pdfile = File.openDialog('Select the PDF file', '*.pdf, *.ai');
var fl = new File(pdfile);
obj.file = fl;
var pref = app.preferences.PDFFileOptions;
pref.pageToOpen = 2; //set page number you want to place.
pref.pDFCropToBox = PDFBoxType.PDFMEDIABOX;
var pdfOptions = app.preferences.PDFFileOptions;
var obj = app.activeDocument.layers[0].placedItems.add();
var pdfile = File.openDialog('Select the PDF file', '*.pdf, *.ai');
var fl = new File(pdfile);
obj.file = fl;