how to solve "stream closed error" in java?

Question

I'm trying to merge multiple pdf files in java using pdfbox jar using this code. when it's trying to merge the second pdf in to first...it's getting Stream closed error. can anyone pls help me with this?

 public static string PDFMergingForForeignModule String(folder_name) {
      //Creating a File object for directory
      String path = "E:\Code";

      File directoryPath = new File(path);
      File[] files = directoryPath.list();
      
      String mergedFileName = "Merged_"+folder_name+".pdf";
      path = path + "\\"+ mergedFileName;
      mergePDFFiles(files, path);
      
  
      File mergedFile = new File(mergedFileName);
     }

public void mergePDFFiles(File[] files, String filepath) throws COSVisitorException{
    try {
        PDFMergerUtility pdfmerger = new PDFMergerUtility();
        for (File file : files) {
            PDDocument document = PDDocument.load(file);
            pdfmerger.setDestinationFileName(filepath);
            pdfmerger.addSource(file);
            pdfmerger.mergeDocuments();
            document.close();
        }
    } catch (IOException e) {
        logger.error("Error to merge files. Error: " + e.getMessage());
    }
}