Dovada achiziției este factura.

Because Romanian usually puts the definite article at the end of the noun.

• dovadă = proof / a proof
• dovada = the proof

So dovada is the definite singular form of the feminine noun dovadă.

It comes from the noun achiziție and is in the genitive singular definite form.

Useful forms:

• achiziție = purchase / acquisition
• achiziția = the purchase
• achiziției = of the purchase / to the purchase

In this sentence, achiziției means of the purchase. Romanian uses this form after dovada to show the relationship between the two nouns.

Because Romanian often expresses of by changing the noun into the genitive case instead of adding a separate word.

So:

• dovada achiziției = the proof of the purchase

English uses a separate word, but Romanian often builds that meaning into the noun ending.

Because the sentence is identifying one specific thing as another specific thing.

• dovada achiziției = the proof of purchase
• factura = the invoice / the bill

After este, Romanian can use a definite noun when the speaker means a specific identified item. Here the idea is not just an invoice in general, but the invoice as the relevant proof.

If you said o factură, that would sound more like an invoice as one possible example, not the specific document being pointed to.

Yes. That is also grammatical.

The difference is mainly one of focus:

• Dovada achiziției este factura.
  Starts with the proof of purchase and then tells you what it is.
• Factura este dovada achiziției.
  Starts with the invoice and then tells you what role it has.

Romanian word order is more flexible than English, so both versions work.

Not exactly.

factură usually means invoice or bill. In some contexts, that document can also serve as proof of purchase, which is why it works here.

Other common Romanian words are:

• bonul fiscal = cash-register receipt
• chitanța = receipt, especially for payment

So the best English translation can depend on the situation.

In a normal full sentence, you should keep este.

Romanian usually does not drop the present tense of to be in standard sentences like this. So:

• Dovada achiziției este factura. = normal and complete
• Dovada achiziției factura. = not standard

You might see omission only in headlines, labels, or very informal shorthand.

A rough English-style pronunciation is:

doh-VAH-dah ah-kee-ZEE-tsi-ey ES-teh fak-TOO-rah

A few helpful sound notes:

• ch before i sounds like k
• ț sounds like ts
• ă is a short neutral vowel, somewhat like the a in about
• ei at the end of achiziției sounds roughly like ey