"It is difficult" is a perfectly correct and usable sentence in written English. It can be used to express that something is hard to do or understand. For example: "It is difficult to find a job these days.".
"It is difficult.
Unfortunately, detecting it is difficult.
"It is difficult," he said.
It is difficult to watch.
He said: "It is difficult.
Even imagining it is difficult.
It is difficult enough.
Awesome tool! I started using it one year ago and I never had to look for another app
Ha Thuy Vy
MA of Applied Linguistic, Maquarie University, Australia