Determine the tempo of the files you need to match using a metronome. In a computer setting, most music sequencers have a “click track” that can be used for this purpose. Let the selection play at normal speed while adjusting the “click” of the metronome until they are aligned. Let it play for several bars to ensure that it is accurate. The tempo of the metronome is the tempo of your audio file. Do this for both files and write down the tempos of each.
Open up a new Pro Tools session. Presumably, you want to match the tempo of one to the other, so you will alter the tempo of only one of these files. Say you have a 105 bpm a capella track and a 95 bpm instrumental, and you want the music set to the tempo of the vocal. Create a 105 bpm session in Pro Tools and import the instrumental audio file. You can set the tempo in the Transport window.
Allow the waveform to load in the Pro Tools session. Select the "Time Shift" option under the Audiosuite menu. Under the time section, enter "95 bpm" as the "Original Tempo" and enter the desired tempo (105 bpm in this case) under "Processed." Click "Process" and give the file a few minutes to undergo the time shift function. Once complete, your 95 bpm instrumental will now play perfectly in pitch at 105 bpm.