Kalau semua dokumen sudah dicetak dan ditandatangani, tinggal masukkan ke amplop lalu kirim besok pagi.

It can be understood either way, but in this sentence it often feels closer to once/when in natural English.

• kalau introduces a condition
• the next action happens after that condition is fulfilled

So this is not a doubtful hypothetical like If it rains.... It is more like:

• If/once all the documents have been printed and signed...

A more formal alternative to kalau is jika.

Sudah marks that the actions are completed.

So:

• sudah dicetak = have already been printed / are done being printed
• sudah ditandatangani = have already been signed

Without sudah, the sentence would be less clearly focused on completion. Here the speaker wants to say that printing and signing must be finished before the next steps happen.

Because they are passive forms.

• dicetak = printed
• ditandatangani = signed

Indonesian often uses the passive when the thing affected is more important than the person doing the action. Here the focus is on semua dokumen, not on who printed or signed them.

Compare:

• Semua dokumen sudah dicetak dan ditandatangani
  focus on the documents

• Kamu sudah mencetak dan menandatangani semua dokumen
  focus on you as the doer

The base expression is tanda tangan, which means signature and also appears in the expression to sign.

The full verb is:

• menandatangani = to sign something

Its passive form is:

• ditandatangani = to be signed

So this is a proper verb formation, not just di + tanda tangan stuck together mechanically.

A useful contrast:

• tanda tangan = signature / signing
• menandatangani dokumen = to sign a document
• dokumen ditandatangani = the document is signed

That is one of its meanings, but not the one used here.

In this sentence, tinggal means something like:

• it only remains to...
• you just need to...
• all that’s left is to...

So:

• tinggal masukkan ke amplop lalu kirim
  = you just need to put it in an envelope and then send it

This use of tinggal is very common in instructions and step-by-step explanations.

Because these are command/instruction forms.

In Indonesian, when giving commands, the meN- prefix is usually dropped:

• memasukkan → masukkan
• mengirim → kirim

So here the speaker is effectively saying:

• put it in an envelope
• then send it tomorrow morning

Also note:

• masuk = to enter / go in
• masukkan = to put something in / insert something

So masukkan is the correct form because the documents are the object being put into the envelope.

The subject is omitted because it is understood from context.

In Indonesian, this is very common, especially in:

• instructions
• reminders
• procedures
• casual spoken directions

The implied subject here is basically you. Depending on context, that could mean:

• you singular
• you all
• you in a neutral formal sense

Indonesian often leaves out subjects when they are obvious.

Both can work, but ke amplop is a concise, natural way to express the destination.

• ke amplop = into/to an envelope
• ke dalam amplop = into the envelope, more explicit

Because masukkan already implies putting something inside, ke amplop is usually enough.

A useful comparison:

• masukkan ke amplop = put it into an envelope
• ada di dalam amplop = it is inside the envelope

So ke is used for movement toward/into something, while di dalam describes location.

Because it is understood from context.

After masukkan, the omitted object is clearly the documents. After kirim, the omitted object is understood as either:

• the documents
• the envelope containing them

Indonesian often leaves out objects when they are already obvious.

A more explicit version would be:

• tinggal masukkan semua dokumen itu ke amplop lalu kirim amplopnya besok pagi

But the original sentence is more natural because it avoids repeating information unnecessarily.

Lalu shows sequence: one action happens after the previous one.

• masukkan ke amplop lalu kirim = put it in the envelope, then send it

If you used dan, it would simply connect the actions, but lalu makes the order clearer.

Compare:

• dan = and
• lalu = then / after that

In step-by-step instructions, lalu is often the better choice.

Because the first part is a conditional clause placed before the main instruction.

Structure:

• Kalau semua dokumen sudah dicetak dan ditandatangani = the condition
• tinggal masukkan ke amplop lalu kirim besok pagi = the main part

Using a comma here is standard and helps readability, much like in English when an if clause comes first.

It is fairly neutral, but it leans a little conversational because of how compact it is.

Features that make it feel natural and efficient:

• omitted subject
• omitted objects
• direct command forms like masukkan and kirim
• kalau instead of the more formal jika

A more formal or polished version might be:

• Jika semua dokumen sudah dicetak dan ditandatangani, silakan masukkan dokumen tersebut ke dalam amplop, lalu kirimkan besok pagi.

That version sounds more official or businesslike.

Besok pagi means tomorrow morning, and here it most naturally modifies kirim.

So the idea is:

• first put the documents in the envelope
• then send them tomorrow morning

Indonesian often places time expressions after the verb they relate to. In this sentence, besok pagi most naturally applies to the sending, not to the putting into the envelope.