Answer: -
Many drugs are sold as their hydrochloric salts (RNH₃⁺Cl⁻), formed by reaction of an amine (RNH₂) with HCl.
It is done because amines are generally liquids. But their hydrochloric salts are solid. A solid drug is always more preferable for drug companies as their handling and packaging are easier.
Acebutolol consists of one amide functionality as well as a secondary amine functionality.
When HCl is added, the lone pairs of the nitrogen of the secondary amine attacks it, leading to the formation of it's hydrochloric salts.