An Arkansas contractor taking work in Pennsylvania deals with the same four questions everywhere: who licenses the trade, when a licence is actually required, when workers compensation kicks in, and where the business registers. Below is Pennsylvania's answer to each, with the agency's own link.
Licensing
Pennsylvania Office of Attorney General, Bureau of Consumer Protection (HICPA registration)
Registration, not licensing: contractors performing $5,000 or more of home improvements per year must register biennially ($100) with the Attorney General under HICPA; registration numbers must appear on advertisements, contracts, estimates, and proposals.
https://www.attorneygeneral.gov/resources/home-improvement-contractor-registration/
Workers compensation
Pennsylvania Department of Labor & Industry, Bureau of Workers' Compensation
Coverage required for any employer with at least one employee who could be injured in Pennsylvania, unless every employee fits a narrow statutory exemption.
Tax registration
Pennsylvania Department of Revenue
https://www.pa.gov/services/revenue/register-my-business-for-taxes
New hire reporting
Most states require newly hired employees to be reported within a short window of their start date.
https://www.pa.gov/services/dli/report-newly-hired-employees
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Starting or running the business itself is covered in the contractor business guide. Arkansas licence records for Benton and Washington counties are in the contractor directory.