TOKYO — Pubcaster NHK said Wednesday it plans to make its programs available for download on the Internet by next April, a first for a Japanese broadcaster, though the BBC will launch a similar service on July 27.A bill to liberalize Japan’s Broadcast Law, which forbids the service, is due to pass in the next session of parliament. Viewers will be able to access programs, beginning with news and documentaries, broadcast the previous week. The content cannot be copied and will be available for only a limited time. If NHK can work out permissions problems with rights holders, it also plans to offer dramas and other entertainment. The service will be free, but NHK may restrict it to viewers who are paying their NHK receiving fees.