What is the difference between the two following sentences?
1) Where did you save that file?
2) Where you saved that file ?
Let's imagine that your friend saved a file somewhere, and you wanted to know where it had been saved. You would ask:
"Where did you save that file?"
Afterwards you might say to your friend:
"I wondered where you saved that file."
If you are asking the question, you cannot say:
"Where you saved that file?"
But you can use those words as part of a sentence, as illustrated.
The correct formal structure of questions (interrogative sentence) of the past simple tense is:
auxiliary verb ➕ pronoun ➕ infinitive verb
and with Wh questions is:
Wh question (adverb) ➕ auxiliary verb ➕ pronoun ➕ infinitive verb
Therefore, the the correct formal interrogative sentence is:
Where did you save that file?
On the other hand, you can use in a statement (declarative sentence) that says:
I am not sure where you saved that file.
In this case, the word "where" is not used as wh question (=adverb) but as conjunction.
So in the end of the day, both are correct depending on the context.
Obviously, it is not possible to ask:
Where you saved that file? ❎