I'd forgotten/I forgot where the old files were

[EngLearner]

John turns on his computer and creates some files for Bob. He tells Bob on the phone that he's created them and where they are. The next day, John forgets where they are, so he creates new files in a different folder. Later that day, when Bob comes to John's house, John opens the folder with the new files and shows them to Bob. Bob hasn't forgotten where the old files are, so he says to John: "Why did you create them again in a different folder?" To which John replies with the following:

I'd forgotten/I forgot where the old files were, so I created the new ones.

Which option should be used in the above sentence? If they're both appropriate, then do you have a preference?

 

[jutfrank]

The past simple suffices here and would perhaps more likely be used for its ease and simplicity, but the past perfect also works well.

It isn't really about preference but about expressing clearly what you mean. If you were a student of mine, I'd encourage you to use the past perfect, as this is a good context in which to practise it.