after as soon as we put always past participle
No. After "as soon as" we normally put a clause. Very often we use the present perfect (that may be what you're thinking of when you say "past participle"), but this isn't always the case:
As soon as I have finished, I will leave the office.
As soon as I finish, I will leave the office.
As soon as he had finished, he left the office.
As soon as he finished, he left the office.
She always leaves the office as soon as she finishes.