Knowing he was on the way, she was happy.

Participle reason adverbials are generally status verbs located at the front of the sentence. Can be changed to an adverbial clause of reason:

Because she knew he was on the way, she was very happy.

The boy sat in the room, reading a book.

The participle accompanying the adverbial generally represents a secondary verb and is located at the end of the sentence. It can be reduced to a coordinate predicate by adding and:

The boy sat in the room and read a book.