Поддоны можно штабелировать.

It is the accusative plural, because поддоны is the thing being stacked.

However, for inanimate masculine nouns like поддон, the accusative plural looks exactly the same as the nominative plural. So:

• nominative plural: поддоны
• accusative plural: поддоны

That is why it may look like the subject at first glance, even though in this sentence it functions as the object.

Можно is a very common Russian word meaning something like:

• it is possible
• it is allowed
• one may / can

It creates an impersonal construction, so Russian does not need a subject like you, they, or it.

So the structure is basically:

• можно + infinitive = it is possible/allowed to do something

In this sentence, it gives the meaning can be stacked or may be stacked.

After можно, Russian normally uses the infinitive to say what action is possible or allowed.

So:

• можно штабелировать = it is possible/allowed to stack

This is one of the most common patterns in Russian:

• можно курить = smoking is allowed / one may smoke
• можно открыть = one can open it
• можно использовать = it may be used

It can mean either, depending on context.

With a sentence like Поддоны можно штабелировать, the meaning is often somewhere between:

• The pallets can be stacked
  and
• The pallets may be stacked

On packaging, labels, or technical instructions, it often implies this is permitted / acceptable / suitable.

So the exact English translation depends on context, even though the Russian wording stays the same.

It is not a normal English-style passive, but it often translates that way.

Literally, the structure is closer to:

• Pallets, it is possible to stack

In natural English, we usually make that passive:

• Pallets can be stacked

So Russian is using an impersonal construction, while English often prefers a passive translation.

Russian word order is flexible, so putting поддоны first gives it emphasis as the topic:

• Поддоны можно штабелировать = As for pallets, they can be stacked

This is especially natural in labels, instructions, and technical writing, where the item being discussed often comes first.

You could also say:

• Можно штабелировать поддоны

That is grammatical too, but it feels a little less like a label or notice about pallets specifically.

Штабелировать is imperfective.

That makes sense because the sentence is stating a general rule or property, not talking about one single completed action.

Russian often uses the imperfective after можно when the meaning is broad or general:

• можно читать = one can read / reading is allowed
• можно хранить = one may store
• можно штабелировать = one may stack / it can be stacked

A perfective verb would sound more like a specific completed result in a particular situation.

It is understandable, but it sounds somewhat technical or industrial.

It comes from штабель, meaning a stack or pile. So штабелировать means to stack in piles / in a stack.

In everyday speech, people might sometimes prefer other wording depending on context, but on packaging, in logistics, warehouses, and manuals, штабелировать is very natural.

Yes. Russian has other possible ways to express a similar idea, depending on style and context.

For example:

• Поддоны можно складывать в штабель = pallets can be piled into a stack
• Поддоны разрешается штабелировать = pallets are permitted to be stacked
• Поддоны допускается штабелировать = pallets may be stacked / it is acceptable to stack them

But Поддоны можно штабелировать is short, clear, and very typical for instructions or labeling.

The stress is:

• поддОны
• мОжно
• штабелировАть

So approximately:

• padd-DO-ny MOZH-na shta-be-li-ra-VAT'

For a learner, the most useful thing is to remember that Russian stress is important and not always predictable, especially in longer verbs like штабелировать.