I have a **text-area** with some content inside. I have another form element that is for **upload xls file**. Now what I want to achieve is, when I click on upload button the xls file content should replace the text-area content. 

    $form['edit_file'] = array(
            '#type' => 'textarea',
            '#required' => TRUE,
            '#rows' => 20,
            '#default_value' => !empty($raw_xml) ? $raw_xml : '',
    //        '#states' => array(
    //            'visible' => array(
    //                ':input[name ="upload_excel_files_upload_button"]' => array('value' => 'Upload'),
    //            ),
    //        ),
            
        );
        
        $form['upload_excel_files'] = array(
            '#title' => t('Upload Excel File'),
            '#type' => 'managed_file',
            '#description' => t('Please upload only .xlsx files.'),
            '#size' => 50,
    //        '#ajax' => array(
    //            'callback' => 'replace_existing_xml_callback',
    //            'wrapper' => 'replace-existing-xml-div',
    //            'method' => 'replace',
    //            'effect' => 'fade',
    //        ),
        );

**How can I replace "edit_file" form item content by uploaded file?? I can't write this logic in form submit handler because on submit, text-area content get saved into database.**

Any help will be highly appreciated. Thanks in advance.