So when you delete a file on a PC it removes the pointer of that file rather than the actual bytes, that remains until it is written over.

If you have a txt that simply has the word "Hello" and I charge the contents to "Aljoe" does this change write over the original bytes of the file or does it just remove the pointer of that and create another file of same attributes but different contents. 

Does this mean that "Hello" txt file is recoverable or has the "Aljoe" text replaced that file.

Hope that makes sense...