当用户更改SaveFileDialog中的另存为类型时更改文件扩展名

SaveFileDialog saveFileDialog = new SaveFileDialog();
saveFileDialog.Filter = "文本文件|*.txt|Word文档|*.docx|PDF文档|*.pdf";
if (saveFileDialog.ShowDialog() == DialogResult.OK)
{
    string selectedFileType = saveFileDialog.Filter.Split('|')[saveFileDialog.FilterIndex * 2 - 1];
    string fileExtension = Path.GetExtension(saveFileDialog.FileName);
    string newFileExtension = Path.GetExtension(selectedFileType);
    string newFilePath = Path.ChangeExtension(saveFileDialog.FileName, newFileExtension);

    // 执行文件扩展名更改操作
    File.Move(saveFileDialog.FileName, newFilePath);
}