Harrad has signed a two-and-a-half year deal to conclude a busy month for Cardoza, who also signed former Southend winger Francis Laurent and tied young talent Michael Jacobs to a new deal.
He said: "We are absolutely delighted to secure Shaun.
"We have been steadfast and determined to make this signing and Shaun has always been our number one target. We have had to work hard, be patient and our hard work has paid off.
"It has been an excellent transfer window so far - we have signed a key striker, we have tied one of our brightest young prospects down to a longer contract, we have handed an exciting young player a professional deal and we have also added Francis Laurent, a player who will excite the crowd and can play at a much higher level."
Source: PA
Source: PA