Whenever I try to fill in a certain part of a pdf form, it automatically fills in other parts with the same thing.

https://answers.acrobatusers.com/Whenever-I-fill-part-pdf-form-automatically-fills-parts-thing-q236415.aspx

If they field names are the same they are technically one field, which an have only one value, so as soon as you change the value it changes the values in all of the identically named fields.