When his wayward pupil Darren Cross (Corey Stoll) discovered the formula, Cross forced Pym out of his own company, leading him to recruit thief Scott Lang (Paul Rudd) to steal back his work and destroy the evidence.
Pym Technologies was founded by Hank Pym (Michael Douglas), the original Ant-Man, and it was the secret home of his most treasured scientific discovery: the Pym Particle.
Evidence, in this case, means the entire building, which imploded on itself thanks to some explosive Pym Particles.
Able to shrink down objects and living creatures, Pym deemed the particles too dangerous to trust with anyone else, and locked them away.