The image in Areeb's answer is helpful but a bit difficult to read. Enhancing the image by balancing the levels produces:
The first item is clearly:
An imprint left behind on a piece of paper beneath the paper being written on. It can be read more easily by rubbing a pencil across it, and features in pretty much every murder mystery ever written (and I'm sure a few real cases too).
The second item:
Is the paper left behind when you peel off a label from an embossing machine. The unique printing method employed by embossing machines leaves a mirrored imprint. The process is explained in more detail here
And the third item appears to be:
The imprint left on a typewriter ribbon (the ink-covered ribbon pressed against the paper when typing the letters). If the ribbon is fresh, or recently wound, it would be possible to see some of what was written by looking at where the ink is slightly depleted.
They're all imprints left behind after writing something, which can be used to determine the content of an otherwise lost or hidden message, or tie a particular document to the location it was written ("why this Will is a fake; it was written on YOUR typewriter points to the murderer")
All of these "office tools" were eventually computerized. Humn said this in chat