Kan du lägga bilagan i samma mapp som kopian?

Because Swedish often adds the definite article to the end of the noun.

• bilaga = attachment / appendix / enclosure
• bilagan = the attachment
• kopia = copy
• kopian = the copy

For common-gender nouns like these, the definite singular ending is usually -n:

• en bilaga → bilagan
• en kopia → kopian

So in this sentence, the speaker is referring to specific things: the attachment and the copy.

Yes, literally Kan du ... ? means Can you ... ?, but in real Swedish it is also a very common way to make a polite request.

So:

• Kan du lägga bilagan ... ?
  = Can you put the attachment ... ? = also naturally Could you put the attachment ... ?

It is not necessarily about ability. Very often it functions as a request, just like English Can you... ?

Lägga means to lay / put / place. It is used when you put something somewhere.

In this sentence:

• lägga bilagan i samma mapp = put the attachment in the same folder

This is a very normal verb for placing something, whether physically or digitally.

A learner should also know the common pair:

• ligga = to lie / be lying (state)
• lägga = to lay / put (action)

Compare:

• Filen ligger i mappen. = The file is in the folder.
• Lägg filen i mappen. = Put the file in the folder.

Because Swedish uses i (in) with mapp (folder) when something is inside it.

• i mappen = in the folder

This works both for:

• a physical folder
• a digital folder

Using på would usually mean on, which does not fit naturally with folder here.

samma means same.

In Swedish, samma does not usually change for gender or number the way many adjectives do. That makes it easier to use than many other adjectives.

Examples:

• samma bok = the same book
• samma bil = the same car
• samma mappar = the same folders

So:

• i samma mapp = in the same folder

Here som means as in the expression the same ... as ...

So:

• samma mapp som kopian = the same folder as the copy

This is a very common pattern in Swedish:

• samma X som Y = the same X as Y

Examples:

• samma rum som jag = the same room as me
• samma dag som igår = the same day as yesterday

It can mean several related things depending on context:

• attachment in an email
• appendix in a document
• enclosure sent with a letter

In this sentence, because we also have mapp (folder), many learners would naturally think of a digital file attachment, but it could also be a physical document in a folder. The sentence itself does not force only one interpretation.

The basic structure is:

• Kan du = modal verb + subject
• lägga = infinitive main verb
• bilagan = object
• i samma mapp som kopian = place expression

So, step by step:

• Kan = can
• du = you
• lägga = put
• bilagan = the attachment
• i samma mapp = in the same folder
• som kopian = as the copy

This word order is very standard for Swedish questions with a verb first:

• Kan du ... ?
• Vill du ... ?
• Har du ... ?

Swedish handles definiteness differently from English.

In English, you say:

• in the same folder

In Swedish, you usually say:

• i samma mapp

Even though English has the, Swedish often does not add the usual definite ending after samma in this kind of phrase.

So samma mapp already works naturally for the same folder.

Yes, placera could work, but it sounds a bit more formal or deliberate.

Compare:

• Kan du lägga bilagan i samma mapp som kopian?
  natural, everyday
• Kan du placera bilagan i samma mapp som kopian?
  correct, but more formal or stiff in many contexts

For ordinary speech, lägga is usually the more natural choice.

Yes. It sounds natural in both cases.

It could refer to:

• putting a paper attachment into a physical folder
• moving a digital attachment into the same computer folder as the copy

Because mapp is used for both folder meanings, the context usually tells you which one is meant.