How to delete attachments in PDF using iText?

public void addAttachments(String src, String dest, String[] attachments)
    throws IOException,DocumentException {
    PdfReader reader = new PdfReader(src);
    PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
    for (int i = 0; i  attachments.length; i++) {
        addAttachment(stamper.getWriter(), new File(attachments[i]));
    }
    stamper.close();
}
protected void addAttachment(PdfWriter writer, File src) throws IOException {
    PdfFileSpecification fs = PdfFileSpecification.fileEmbedded(
        writer, src.getAbsolutePath(), src.getName(), null);
    writer.addFileAttachment(
        src.getName().substring(0, src.getName().indexOf('.')), fs);
}

Let me start by rewriting your code to add an embedded file.

public void manipulatePdf(String src, String dest) throws IOException, DocumentException {
    PdfReader reader = new PdfReader(src);
    PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
    PdfFileSpecification fs = PdfFileSpecification.fileEmbedded(
            stamper.getWriter(), null, "test.txt", "Some test".getBytes());
    stamper.addFileAttachment("some test file", fs);
    stamper.close();
}

You can find the full code sample here: AddEmbeddedFile

Now when we look at the Attachments panel of the resulting PDF, we see an attachment test.txt with description "some test file":

Attachment shown in Adobe Acrobat

After you have added this file, you now want to remove it. To do this, please use RUPS and take a look inside:

Attachment shown in iText RUPS

This gives us a hint on where to find the embedded file. Take a look at the code of the RemoveEmbeddedFile example to see how we navigate through the object-oriented file format that PDF is:

public void manipulatePdf(String src, String dest) throws IOException, DocumentException {
    PdfReader reader = new PdfReader(src);
    PdfDictionary root = reader.getCatalog();
    PdfDictionary names = root.getAsDict(PdfName.NAMES);
    PdfDictionary embeddedFiles = names.getAsDict(PdfName.EMBEDDEDFILES);
    PdfArray namesArray = embeddedFiles.getAsArray(PdfName.NAMES);
    namesArray.remove(0);
    namesArray.remove(0);
    PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
    stamper.close();
}

As you can see, we start at the root of the document (aka the catalog) and we walk via Names and EmbeddedFiles to the Names array. As I know that the embedded file I want to remove is the first in the array, I remove the name and value by removing the element with index 0 twice. This first removes the description, then the reference to the file. The attachment is now gone:

Attachment is gone in Adobe Acrobat

As there was only one embedded file in my example, I now see an empty array when I look inside the PDF:

Empty array in iText RUPS

If you want to remove all the embedded files at once, the code is even easier. That is shown in the RemoveEmbeddedFiles example:

public void manipulatePdf(String src, String dest) throws IOException, DocumentException {
    PdfReader reader = new PdfReader(src);
    PdfDictionary root = reader.getCatalog();
    PdfDictionary names = root.getAsDict(PdfName.NAMES);
    names.remove(PdfName.EMBEDDEDFILES);
    PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
    stamper.close();
}

Now we don't even look at the entries of the EmbeddedFiles dictionary. There is no longer such an entry in the Names dictionary:

No embedded files in iText RUPS