Q:

Usage Difference between to-infinitive and participle

I came across this question today.

Q: the correct expression for blank.

The documents ____ immediate attention are on top.

1. Requiring 2. To require

I know the answer is 1. Requiring, however I don't know why number 2 can't be an answer.
As far as I know, a to-infinitive can define a noun, like "books to read," so to me, number 2 can be an answer. But at the same time, I know "documents to require" looks very awkward. I just don't know why. Could you help me?

A:

You are right, in some cases you can use to+infinitive to describe a noun:

I have books to read, work to do, people to call.

However, this only works with verbs that imply the action would be performed with the references nouns being the object of the action. That means that if I describe the actions from my earlier example being executed:

I read books.
  I do work.
  I call people.

If the noun that you describe would be the subject of the action, this doesn't work:

Documents require attention.
  People read books.

In these cases you cannot describe documents or people using to+infinitive:

*Documents to require attention
  *People to read books

Instead, we use the active or present participle to describe them:

Documents requiring attention
  People reading books

