Non-systematic Uses of Acabar

Question 1

Acabar

Answer 1

To finish; to end

Question 2

Present form of Acabar +de + infinitive =

Answer 2

To have just done something.

Example:
Acaban de firmar el tratado.
They have just signed the treaty

Question 3

Imperfect form of acabar +de + infinitive=

Answer 3

“To had just done something.” Past tense.

Example:
“Acababan de firmar el tratado.”
They had just signed the treaty