Learn Icelandic: Við munum hafa skjalfest framvinduna á morgun. - We will have documented the progress tomorrow.

It uses three parts: the auxiliary verb munu conjugated for the subject (við munum = we will), followed by the infinitive hafa (to have), and finally the supine form of the main verb, skjalfest (documented). This structure explicitly expresses an action that will be completed by a certain time in the future.

What is the root of the verb skjalfesta and why is its supine form skjalfest?

It is a compound of the noun skjal (document) and the verb festa (to fasten or fix). Because the supine form of festa is fest, the compound becomes skjalfest after the auxiliary verb hafa.

Why is framvinduna in the accusative case here?

It is the direct object of the verb skjalfesta, which governs the accusative case. The base noun is the feminine framvinda (progress). When you apply the accusative definite article suffix to it, it becomes framvinduna (the progress).

Could we just use the present perfect instead of the future perfect here?

Yes, in daily speech, Icelanders often use the simple present perfect (við höfum skjalfest framvinduna á morgun) to mean the same thing. However, using munum hafa adds a deliberate emphasis, making it absolutely clear that the focus is on the future completion of the task.