Learn Italian: Questi documenti vanno timbrati immediatamente. - These documents must be stamped immediately.

Using andare as the auxiliary verb in a passive sentence creates what is called the "deontic passive" (expressing duty or necessity). Saying vanno timbrati means exactly the same thing as devono essere timbrati (they must be stamped), but it is very common and often sounds more natural in everyday Italian when giving instructions or stating rules.

Why does timbrati end in -i?

Because this is a passive construction, the past participle (timbrato) acts like an adjective. It must agree in gender and number with the subject receiving the action. Since documenti is masculine plural, timbrato becomes timbrati.

Could I use this same structure in a compound tense, like the passato prossimo, to say they "have had to be stamped"?

No. The andare + past participle structure for expressing obligation can only be used in simple tenses (like the present, imperfect, or future). To express this in a compound tense, you would have to go back to using the verb dovere.

How would you express this exact same rule using the active voice?