I said I would file it on Thursday.

Question

1.I said I would file the pictures of Thursday.

2. I said I would file Adriana's work on Thursday.

Answer 1

On Thursday I will file the pictures.

I said on Thursday that I would file the pictures the next day.

Answer 2

In the first sentence, the "it" has no clear referent — we don't know what it refers to. The clearest information might be indicated by:

"I said I would file Adriana's pictures this Thursday."

This indicates whose work it is, what type of work it is, and which Thursday is meant.

This article might be helpful:

http://www.members.cox.net/dagershaw/lol/MessageAcross.html

I hope this helps a little more. Thanks for asking.