import com.spire.pdf.attachments.PdfAttachmentCollection;

public class DeleteAttachments {

    public static void main(String[] args) {

        //load a PDF document
        PdfDocument doc = new PdfDocument();
        doc.loadFromFile("C:\\Users\\Administrator\\Desktop\\Attachments.pdf");

        //get the attachments collection, not containing annotation attachments
        PdfAttachmentCollection attachments = doc.getAttachments();
        
        //remove all attachments
        attachments.clear();

        //remove a specific attachment
        //attachments.removeAt(0);

        //save to file
        doc.saveToFile("output/DeleteAttachments.pdf");
        doc.close();
    }
}

import com.spire.pdf.annotations.PdfAnnotation;
import com.spire.pdf.annotations.PdfAnnotationCollection;
import com.spire.pdf.annotations.PdfAttachmentAnnotationWidget;

public class DeleteAnnotationAttachments {

    public static void main(String[] args) {

        //load a PDF document
        PdfDocument doc = new PdfDocument();
        doc.loadFromFile("C:\\Users\\Administrator\\Desktop\\Attachments.pdf");

        //loop through the pages
        for (int i = 0; i < doc.getPages().getCount(); i++) {

            //get the annotations collection
            PdfAnnotationCollection annotationCollection = doc.getPages().get(i).getAnnotationsWidget();

            //loop through the annotations
            for (Object annotation: annotationCollection) {
                
                //determine if an annotation is an instance of PdfAttachmentAnnotationWidget 
                if (annotation instanceof PdfAttachmentAnnotationWidget){
                    
                    //remove the attachment annotation
                    annotationCollection.remove((PdfAnnotation) annotation);
                }
            }
        }

        //save to file
        doc.saveToFile("output/DeleteAnnotationAttachments.pdf");
        doc.close();
    }
}