How to make an item name from the listbox as a file name?

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C#

named

Dear Experts,

Please, help me resolve an issue in Visual Studio #C.
I am creating utility for renaming of names of multiple files.
Main idea = user opens the folder with files and selects required files for renaming in listbox.
Selection can be performed via searching by special words in names of items (masks "MD").
I have completed work at filtrating names of files and changing their names in listbox. But my problem - I cannot copy name of items and save these as names of files in folder.
Have you ever been observed such problem?
Please help me in solution.

What I have tried:

public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
           if (folderBrowserDialog1.ShowDialog() == DialogResult.OK)
            {

                listBox1.Items.Clear();

                string[] files = Directory.GetFiles(folderBrowserDialog1.SelectedPath);
                string[] dirs = Directory.GetDirectories(folderBrowserDialog1.SelectedPath);
                SelectedPathText.Text = folderBrowserDialog1.SelectedPath;

                foreach (string file in files)
                {
                    listBox1.Items.Add(Path.GetFileName(file));
                }
                foreach (string dir in dirs)
                {
                    listBox1.Items.Add(Path.GetFileName(dir));
                    SelectedPathText.Text = Path.GetFileName(dir);
                }
            }
        }

        private void button3_Click(object sender, EventArgs e)
        {
            timer1.Enabled = true;
            DialogResult result = MessageBox.Show("Are you sure ?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Warning);
            if (result == DialogResult.Yes)
            {
                timer1.Enabled = true;

                try
                {
                                
                    if (checkBox1.Checked)
                    {
                        int SelectedItem = listBox1.SelectedIndex;
                        listBox1.Items.RemoveAt(SelectedItem);
                        listBox1.Items.Insert(SelectedItem, (textBox_rig.Text + ("_" + (textBox_field.Text + ("_" + (textBox_pad.Text + ("_" + (textBox_well.Text + ("_" + (comboBox1.Text  +("_"   +("_"+ (comboBox2.Text + ("_" + ("MD"+ ("_"+ (textBox_start.Text + ("-" + (textBox_end.Text + (".PDF"))))))))))))))))))));
                        
                    }

                }
                catch
                {
                    Application.DoEvents();
                }

               
            }
        }