After you find the microfilm you can read it with the microfilm reader.
Use the reader and use the microfilm on the peg.
This is the low-spoiler guide for "Using the microfilm reader" puzzle in Nine Noir Lives. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.