Cant edit a pdf/a file even after converting it to normal pdf

hello guys, has anyone experienced a problem with editing file. i have downloaded a form on korean embassy's in los angeles website and it is in pdf/a format and i am supposed to fill it in and i cant edit it at all. forst time i see the issue. i converted it to normal pdf but still cant access it. what do i need to do? i spent two days searching google and still facing the same problems. please help guys. i would appreciate any advise. thank you.