Eu copiei o texto, mas esqueci de colar na planilha.

Yes, you could leave out eu.

Portuguese often drops subject pronouns when the verb form already makes the subject clear. Since copiei and esqueci clearly mean I copied and I forgot, eu is optional.

• Eu copiei o texto... = a little more explicit, maybe slightly more emphatic
• Copiei o texto... = very natural in everyday speech

Portuguese uses subject pronouns more than Spanish does, but less than English does.

Both are in the pretérito perfeito, the tense usually used for completed past actions.

• copiei = I copied
• esqueci = I forgot

This tense is used because both things happened as completed events in the past:

1. first, the person copied the text
2. then, they forgot to paste it

Portuguese uses definite articles much more often than English.

So o texto literally means the text, and in many contexts Portuguese prefers the article where English might not be as strict or might phrase things differently.

In computer-related contexts, copiar o texto sounds very natural:

• Copiei o texto
• Apaguei o arquivo
• Abri a planilha

Leaving out the article here would usually sound less natural.

Because the verb esquecer commonly takes de + infinitive when it means to forget to do something.

So:

• esqueci de colar = I forgot to paste
• esqueci de ligar = I forgot to call / turn on
• esqueci de estudar = I forgot to study

This is a very important pattern:

• esquecer de + infinitive

A native English speaker often wants to say something like esqueci colar, but that is not the standard form here.

In standard Portuguese, no. The normal form is esqueci de colar.

You should learn esquecer de as a set pattern when it is followed by a verb:

• Esqueci de responder
• Esqueci de fechar a janela
• Esqueci de colar na planilha

Because the object is understood from the previous part of the sentence.

The first clause already mentions o texto, so the second clause can omit it:

• Eu copiei o texto, mas esqueci de colar na planilha

This is natural because everyone already knows what was supposed to be pasted.

You could also say:

• Eu copiei o texto, mas esqueci de colar o texto na planilha

But that sounds more repetitive. Portuguese often leaves out repeated information when it is obvious.

Yes. Colar literally can mean to glue or to stick, but in computer language it also means to paste.

So in tech contexts:

• copiar = to copy
• colar = to paste

This is exactly like English, where paste originally has a physical meaning but is also used digitally.

Na is a contraction of em + a.

• em = in / on / into, depending on context
• a = the (feminine singular article)

Since planilha is feminine, you get:

• em a planilha → na planilha

So:

• na planilha = in the spreadsheet / into the spreadsheet

This kind of contraction is extremely common in Portuguese:

• no = em + o
• na = em + a
• nos = em + os
• nas = em + as

Because planilha is a feminine noun in Portuguese, so it takes:

• a planilha
• na planilha
• essa planilha

There is no deeper reason you need for this sentence beyond memorizing the noun with its article:

• a planilha = spreadsheet

As a learning habit, it is very helpful to memorize nouns together with their article, not alone.

In modern Brazilian Portuguese, planilha very commonly means spreadsheet, especially in work, school, and computer contexts.

For example:

• abrir a planilha
• editar a planilha
• preencher a planilha

Depending on context, it can also refer more generally to a structured table or worksheet, but spreadsheet is the most likely meaning here.

Mas means but and introduces a contrast.

The contrast is:

• I copied the text
• but I forgot to paste it into the spreadsheet

So mas connects two related ideas where the second one goes against what you might expect from the first.

Yes. Both are common:

• esqueci de colar
• me esqueci de colar

In Brazilian Portuguese, both are used, and the version without me is very common in everyday speech.

So these are both natural:

• Eu esqueci de colar na planilha
• Eu me esqueci de colar na planilha

The original order is very natural, but some variation is possible.

Natural version:

• Eu copiei o texto, mas esqueci de colar na planilha.

Also possible:

• Copiei o texto, mas esqueci de colar na planilha.
• Eu esqueci de colar o texto na planilha, mas copiei o texto.
  This is grammatical, but the emphasis changes and it sounds less natural for the same situation.

In normal conversation, the original sentence is probably the most straightforward way to say it.

Very close to the original. Brazilians might naturally say:

• Copiei o texto, mas esqueci de colar na planilha.
• Eu copiei o texto, mas esqueci de colar.
  if na planilha is already understood

In speech, people often omit eu and sometimes omit other obvious information if the context is clear. The original sentence already sounds completely natural and conversational.