How to Add an Attachment to PDF in Java. For further details: https://kb.conholdate.com/total/java/how-to-add-an-attachment-to-pdf-in-java/

how-to-add-an-attachment-to-pdf-in-java.java

import com.aspose.pdf.*;
public class Main {
    public static void main(String[] args) throws Exception {// Attach file in PDF using Java

        // Load a license
        License lic = new License();
        lic.setLicense("Aspose.Total.lic");

        // Instantiate a FileSpecification object
        FileSpecification fs = new FileSpecification("sample.xlsx", "Sample Excel File");

        // Load the PDF
        Document doc = new Document("Input.pdf");

        // Add attachment
        doc.getEmbeddedFiles().add("1", fs);

        // Save the document
        doc.save("AddAttachment.pdf");

        System.out.println("Done");
    }
}