PDFRenamer.groovy renames PDF file to the file by its Title metadata.

PDFRenamer

// PDF Renamer : Rename PDF file from the metadata Title
// 1: set PATH to pdftk
// 2: plase PDFRenamer.groovy (this file to same directory of pdftk )
// 3: move to the root of target PDF directory
// 4: start PDFRenamer.groovy in pdftk directory

@Grab('net.java.dev.jna:jna:3.4.0') // since Java does not have directory moving function

import com.sun.jna.*;
import com.sun.jna.win32.*;

// pdftk is a must  http://www.pdflabs.com/tools/pdftk-the-pdf-toolkit/
def pathToPdftk ="c:\\where\\tool\\exists\\pdftk"

interface Kernel32Library extends StdCallLibrary {
   Kernel32Library INSTANCE = Native.loadLibrary("kernel32", Kernel32Library.class);
   boolean SetCurrentDirectoryA(String dir);
}

new File(".").eachFileRecurse { file -> 
   if(file.name.endsWith("pdf")) { 
     println file.getPath() +" を調査中"
     Kernel32Library.INSTANCE.SetCurrentDirectoryA(file.getParent())
     "cmd /c echo InfoKey: Title > metadata.txt".execute().text
     "cmd /c echo InfoValue: ZZZ >> metadata.txt".execute().text
     "${pathToPdftk} ${file.getName()} dump_data output metadata.txt".execute().text
     if (getTitle().size()>19) {  // Al least 20 charas new file name should have.
         println "${file.getName()} renamed to ${getTitle()} "
          file.renameTo( new File(file.getParent()+"/${getTitle()}.pdf") )
     }
    
   }
}

///////////////////

def getTitle() {
    nextLine=0
    bookTitle=""
    new File("metadata.txt").eachLine { file, count  -> 
        if (nextLine==1) { 
            nextLine=0
            bookTitle=file.toString().replaceAll(/InfoValue: (.*)/) {m0, m1 -> "${m1}" }
            bookTitle=bookTitle.tr(' ','_')
        }
        if (file.toString() =~/Title$/)  { nextLine=1}
    }   
    return bookTitle
}