Participial adjectives are hard to distinguish because often, they look like verbs, past participles, and other adjectives.
This is because they often end in –er or –ing.
Some exceptions to the rules include misunderstood and unknown, which also function like participle adjectives even though they do not end in –ed.
They are called participial adjectives because they have the same endings as verb participles.
These adjectives function like any other adjective: they help to describe a noun. They might come from a verb form, or they might merely imitate the structure, but they always function as a descriptive adjective.
The tempting glass of water made my mouth salivate.
The fascinating book was a thrilling read. 
The interesting movie made a compelling point.
Amy was bored by the play.
She is tired today, and her work is really tiring.
My frustrating experience at school made me angry.
I have been agitated long enough. 
Some participial adjectives have no corresponding verb form since they are made by putting a noun with a participle, such as:
"drug-induced coma" or "energy-saving technology."
Participial adjectives can be modified to increase or decrease their intensity and used  to compare different nouns. It can be done by using the words very, extremely, less, or by forming comparative and superlative forms. 
Example (using the adjective "annoying"):
Annoying - very annoying - extremely annoying - less annoying - more annoying - the most annoying/