Non dimenticarti di scrivere il nome sul documento.

Dimenticarti comes from the verb dimenticarsi, which means to forget.

• dimenticare = to forget
• dimenticarsi = to forget / to forget something, very common in everyday Italian
• -ti = yourself / you for tu

So in this sentence, dimenticarti is the infinitive + attached pronoun, and it means something like to forget addressed to you.

English usually does not use a reflexive form here, so Italian dimenticarti is normally just translated as forget, not forget yourself.

Both are possible.

With a negative command for tu, Italian very often uses:

• non + infinitive

So:

• Non dimenticarti = very natural
• Non ti dimenticare = also correct

The difference is mainly in structure:

• dimenticarti = pronoun attached to the infinitive
• ti dimenticare = pronoun placed before the verb

In modern Italian, Non dimenticarti... is extremely common and sounds very natural.

Because in this kind of negative tu command, the verb is often in the infinitive, and pronouns can attach directly to an infinitive.

So:

• dimenticare + ti → dimenticarti

This is a standard pattern in Italian:

• ricordarti
• alzarti
• metterti
• prepararti

So Non dimenticarti follows a very normal grammar pattern.

Because after dimenticare or dimenticarsi, Italian normally uses di + infinitive when you mean to forget to do something.

Pattern:

• dimenticare di + infinitive
• dimenticarsi di + infinitive

Examples:

• Ho dimenticato di chiamarti.
• Mi sono dimenticato di studiare.
• Non dimenticarti di firmare.

So here:

• di scrivere = to write

This is why the sentence has Non dimenticarti di scrivere...

Yes, absolutely.

Both are correct:

• Non dimenticare di scrivere il nome sul documento.
• Non dimenticarti di scrivere il nome sul documento.

The version with dimenticarti is very common in spoken Italian and can sound a little more personal or idiomatic. The version without the reflexive pronoun is slightly simpler, but both are natural.

Because in Italian, the possessive is often omitted when it is already obvious from the context.

In a sentence like this, everyone understands that the person has to write their own name, so il nome is enough.

Both are possible:

• scrivere il nome
• scrivere il tuo nome

But il nome sounds very natural in instructions, forms, and everyday reminders.

Sul is a contraction of:

• su + il → sul

So:

• sul documento = on the document

This is the same kind of contraction as:

• nel = in + il
• del = di + il
• al = a + il

Other forms of su include:

• sulla
• sui
• sugli
• sulle

Because su is the normal choice when you mean writing something on a document, form, page, or sheet.

• sul documento = on the document
• nel documento = in the document

Nel documento would sound more like something contained inside the text or contents of the document. But if you are being told where to physically write your name, sul documento is the natural choice.

It is informal singular, because it is addressed to tu.

The clue is -ti, which refers to you in the informal singular form.

A formal version would be something like:

• Non si dimentichi di scrivere il nome sul documento.

An informal plural version would be:

• Non dimenticatevi di scrivere il nome sul documento.

So the original sentence is something you would say to one person you address as tu.

Yes. It is giving a command or reminder: don’t forget...

More specifically, it is a negative command addressed to tu.

Italian negative tu commands often use:

• non + infinitive

That is why you get:

• Non dimenticarti...

instead of a regular imperative form.

So even though dimenticarti looks like an infinitive form, the whole sentence functions as a command.