While a technical person will likely understand, it is better to avoid misinterpretation by rephrasing it.
Similar sentence examples:
The ship was departing laden against a strong wind.
Caren stared puzzled at John.
The confusion in your sentence comes from the fact that "bent" (the Past Participle) is an homograph of the noun "bent". Perhaps the word "curved" as suggested by 'user8543', can make the grammatical structure a bit clearer. If there is a sharp corner in the "first surface", use "angled".
Another note, do you need to use Present Continuous? It seems that Present Indefinite would be simpler
a first surface extends bent from a second surface
And why is there 'a' in front of "first surface"?