Can you save to file and edit file?

I have this problem with a dummy site i'm working on (for learning purposes) and i have 20 form text fields with an "add extra field" button. They are for entering sales of products, but the problem i'm having is that i use a DB, but come to realize that anything greater then 20 entries won't work if i want to use a DB. So i was wondering if you can save the information given from the form fields onto a file of some sort (like excel or pdf), but later on if i want to make a change to an entry on that file would it be possible to recall the file and make the changes accordingly without rewriting the entire thing?

Hope that makes sense. thx