Download and open the latest version of iTunes media player. Load the MP3 file by selecting "Add File to Library..." in the "File" menu or dragging and dropping the file into the program window.
Select "Preferences" from the "Edit" menu. Under the "General" tab click the button marked "Import Settings." In the "Import Using" selection box, choose "WAV Encoder." Leave the "Setting" box marked "Automatic." Click "OK" and exit the "Preferences" screen.
Right-click the song you wish to convert and choose the "Create WAV Version" option from the box that pops up. An orange "Converting..." box will pop up in the left iTunes panel. Wait for it to disappear.
Click or copy the Thompson Demo mp3PRO Player/Encoder link in the Resources section below. At the page that loads click the "free download" link and run the installer file that downloads.
Follow the on-screen instructions to install the program to your PC. When installation is complete, open the program.
Click the "encode" button in the Thompson Demo screen. In the window that pops up click the "..." button next to the "Input" box. Select the WAV file you saved on your PC in Step 3. Leave the "Output" box at the default setting to save the MP3Pro in the same folder as the WAV or click the "..." button next to it to choose a different location on your PC. Ignore the check boxes.
Click "ENCODE" at the top of the screen. When the progress bar at the bottom completes, your MP3Pro file will be stored at the location you selected in the "Output" box.