Is it permissible for a man to look at the clothes of a non-mahram woman and touch them, even if he knows this woman?

The basic principle concerning things is permissibility, unless there is evidence indicating their prohibition. Accordingly, if the mentioned clothes were not being worn by their owner at the time of touching or holding them, and if touching or looking at them did not lead to arousal or temptation, then there is no harm in that. However, if any of these conditions are not met, then it is not permissible.