Limits

Three documents that should not become text

The tool will produce something in each of these cases. That something will not be useful.

A scan

There is no text in a scanned page — only an image that resembles one. Nothing comes out.

A form

A form's meaning lives in which box a value sits in. Strip the boxes and you have a list of words and numbers with no relationship between them.

Anything where position is the content

Org charts, floor plans, timetables. The layout was the message.

For the second and third, a conversion to Word or Excel keeps the structure instead of discarding it, which is usually what was actually wanted.