use this script

// Complements: Planet PDF (http://www.planetpdf.com/)

// Modified by Jeff Baitis for Acrobat 9 and Acrobat X compatibility

// Improved Collate function with status bar.

// Add a menu item to reverse all pages in the active document

app.addMenuItem({ cName: "Reverse", cParent: "Edit", cExec: "trustedReversePages();", cEnable: "event.rc = (event.target != null);", nPos: 0 });

// Add a menu item to collate with another document on the filesystem

app.addMenuItem({ cName: "Collate", cParent: "Edit", cExec: "trustedCollatePages();", cEnable: "event.rc = (event.target != null);", nPos: 0 });

trustedReversePages = app.trustedFunction(function()

{

app.beginPriv(); // Explicitly raise privileges

var t = app.thermometer;

t.duration = this.numPages;

t.begin();

for (i = this.numPages - 1; i >= 0; i--)

{

t.value = (i-this.numPages)*-1;

this.movePage(i);

t.text = 'Moving page ' + (i + 1);

}

t.end();

app.endPriv();

})

// Collating pages

/*

Title: Collate Document

Purpose: User is prompted to select document to insert/collate.

Author: Sean Stewart, ARTS PDF, www.artspdf.com

*/

trustedCollatePages = app.trustedFunction(function()

{

app.beginPriv(); // Explicitly raise privileges

// create an array to use as the rect parameter in the browse for field

var arRect = new Array();

arRect[0] = 0;

arRect[1] = 0;

arRect[2] = 0;

arRect[3] = 0;

// create a non-visible form field to use as a browse for field

var f = this.addField("txtFilename", "text", this.numPages - 1, arRect);

f.delay = true;

f.fileSelect = true;

f.delay = false;

// user prompted to select file to collate the open document with

app.alert("Select the PDF file to merge with")

// open the browse for dialog

f.browseForFileToSubmit();

var evenDocPath = f.value;

var q = this.numPages;

var t = app.thermometer;

t.duration = q;

t.begin();

// insert pages from selected document into open document

for (var i = 0; i < q; i++) {

var j = i*2;

this.insertPages(j, evenDocPath, i);

t.value = i;

t.text = 'Inserting page ' + (i+1);

}

t.end();

// remove unused field

this.removeField("txtFilename");

app.endPriv();

Closing this issues, as no information was provided.