Is ptsd just a less severe form for borderline personality disorder?

No: These are completely different disorders. Ptsd is an axis i disorder with discrete criteria for having witnessing or experiencing an actual or perceived traumatic event with symptoms presenting greater than 30 days from said event. Borderline personality disorder is a condition which evolves over time and not from one specific discrete event.

No : U ask an interesting question because pts with bpd often have a history of childhood trauma.

BPD: No, but the 2 can coexist.

Oh my, no!!: Although both are associated with trauma at some point in life, they are entirely different conditions. Borderline personality disorder is about a person's life long character and behaviors. Post traumatic stress disorder is a series of disabling symptoms that can develop after being exposed to a life-threatening or horrific trauma (or traumas). They may co-exist.