how do i know if my former employer is an at will company

Pennsylvania is an "at-will" employment state, which means that unless you (1) have an employment contract that specifies under what conditions you can be terminated; (2) are a member of a union subject to a collective bargaining agreement; or (3) work for a government entity with a protected property interest in your job, then you are considered to be an "at-will" employee by default.  Therefore, unless you fall into one of the categories I mentioned, there is a strong possibility that you were "at-will" at your former employer.  And, in an at-will employment state such as Pennsylvania, an employer can terminate you for good reason, bad reason, or no reason whatsoever, so long as it is not discriminatory or retaliatory as defined under Pennsylvania or Federal law.  An employer is also not legally required to give you a reason for your termination.