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Hello @speckpgh ,
Several people have said “Yes”, you can use that substitute C chord. But I will reinforce that.
First, let’s identify that chord. There is no such thing as an “add 7”, because 7th chords are a chord staple, not an extension. There are major 7ths and dominant 7ths. They are created by adding a fourth note to your triad chord. If that 4th note is one half step from the chord’s root, it’s a major 7 chord. If the 4th note is 2 half steps, or a whole tone, from the chord’s root, it’s a dominant 7, sometimes called a flatted 7th.
Now, one of the common teaching methods is to show beginners simplified chord shapes so they can realistically play a simple song. As their fingers gain more dexterity and independence, those more difficult shapes start to get easier to learn. There is no “danger” in doing this. In fact, just the opposite. Since it will increase your fun it will also increase your improvement. And, it will increase that time it takes to learn chord shapes. You will learn the C maj7 faster than the standard C shape, and you will later learn the standard C shape faster as your fingers will have had the chance to gain dexterity and independence.
So have fun and start playing songs.
MG 😀