jungyohan munseoneun poldeoreul ttaro mandeureoseo jeojanghae dwo.

문서는 uses the topic marker 는, not the object marker 를.

Here, 중요한 문서는 means something like:

• as for important documents
• when it comes to important documents

So the sentence sets important documents as the topic, and then gives advice about what to do with them.

A very literal breakdown is:

• 중요한 문서는 = as for important documents
• 폴더를 따로 만들어서 저장해 둬 = make a separate folder and save them there / keep them saved

If you used 문서를, the sentence would feel more like it was focusing directly on important documents as the object of the action, rather than introducing them as the topic.

In Korean, nouns often do not need a plural marker even when they refer to multiple things.

So 중요한 문서 can mean:

• an important document
• important documents

The context tells you which is intended. In this sentence, it most naturally means important documents in general.

You could say 중요한 문서들은 to make the plural more explicit, but Korean often leaves that unstated when it is already obvious.

따로 means separately, apart, or in a separate way.

In 폴더를 따로 만들어서, it means:

• make a folder separately
• make a separate folder
• create a folder just for that purpose

So the idea is not just make a folder, but make a separate folder for important documents.

Common similar uses:

• 따로 보관하다 = keep separately
• 따로 정리하다 = organize separately
• 따로 말하다 = say separately / discuss separately

Both are possible, but they feel slightly different in flow.

폴더를 따로 만들어서 uses -아서/-어서 to connect actions:

• make a separate folder, and then save [the documents]

It has a natural step 1 -> step 2 feeling.

따로 폴더를 만들고 저장해 둬 is also grammatical and means roughly the same thing:

• make a separate folder and save them

But 만들어서 often sounds a bit smoother when one action is done in preparation for the next. You make the folder first, and that leads into the saving.

In 만들어서, the ending -어서 connects 만들다 to the next verb.

So:

• 만들어서 저장해 둬 = make [it], and then save [them] = after making [it], save [them]

This form can show:

• sequence: one thing happens, then the next
• method or means: do something by means of the first action
• natural connection between actions

Here it mainly shows sequence/preparation:

1. create a separate folder
2. save the important documents there

The object is omitted because it is understood from context.

The sentence topic is 중요한 문서는, so after that, Korean does not need to repeat 문서를 again.

A fuller version could be:

• 중요한 문서는 폴더를 따로 만들어서 저장해 둬.

This is understood as:

• As for important documents, make a separate folder and save them there / keep them saved.

Korean often drops things that are already clear from context, especially:

• subjects
• objects
• locations
• pronouns

This is one of the most useful parts of the sentence.

저장하다 simply means to save.

저장해 두다 means more like:

• save and leave it that way
• save it in advance
• keep it saved
• put it away for later use

The grammar -아/어 두다 adds the nuance of doing something now so that the result remains useful later.

So:

• 저장하다 = save
• 저장해 두다 = save it and keep it there / save it ahead of time

In this sentence, that nuance fits well because important documents should be stored safely and kept organized for future use.

둬 is a contracted spoken form.

The full form is:

• 두어 from 두다

But in everyday Korean, 두어 commonly contracts to 둬.

So these are related:

• 저장해 두어 -> full connected form
• 저장해 둬 -> common contraction in speech

Also, the sentence ends with 둬, which gives it a casual conversational tone, like telling a friend, younger person, or someone close:

• Save them in a separate folder, okay?
• Make a separate folder and keep them saved there.

A more polite version might be:

• 중요한 문서는 폴더를 따로 만들어서 저장해 두세요.

Yes. 저장해 놓다 is also possible, and it is very close in meaning to 저장해 두다.

Both -아/어 두다 and -아/어 놓다 can mean doing something in advance and leaving it in that state.

Very roughly:

• -아/어 두다 often emphasizes keeping something ready / set aside
• -아/어 놓다 often emphasizes the resulting state after doing it

In many everyday situations, they overlap a lot.

So these are both natural:

• 저장해 둬
• 저장해 놔

But 저장해 두다 sounds especially natural for something you keep prepared or stored for later.

This sentence is in a casual, non-polite style.

The ending -둬 is informal, so it would typically be used with:

• close friends
• younger people
• children
• someone you speak casually with

It would not usually be appropriate in formal situations or with someone you should speak politely to.

Polite versions could be:

• 중요한 문서는 폴더를 따로 만들어서 저장해 두세요.
• 중요한 문서는 폴더를 따로 만들어서 저장해 두는 게 좋아요.

So the original sentence sounds like a straightforward instruction or piece of advice in casual speech.

Korean often omits the subject when it is understood from context.

In this sentence, the implied subject is probably:

• you

So the meaning is something like:

• For important documents, make a separate folder and save them there.

Depending on context, it could also be general advice, like:

• Important documents should be saved in a separate folder.

But because of the casual ending 둬, it most naturally sounds like the speaker is telling someone directly what to do.

Because 폴더 is the object of 만들다.

• 폴더를 만들다 = make/create a folder

So in the phrase:

• 폴더를 따로 만들어서

the folder is the thing being created, which is why it takes 를.

The sentence has:

• 문서는 as the topic
• 폴더를 as the object of 만들다

This is a good example of how a Korean sentence can have a topic marked with 은/는 and also an object marked with 을/를 in the same sentence.

It is somewhere between a casual command and practical advice.

Because the ending is informal and direct, it can sound like:

• Do this.
• You should do this.
• Make a separate folder and save them there.

Whether it feels more like a command or advice depends on tone and context.

For example:

• said by a parent to a child -> more command-like
• said by a friend giving computer-organizing advice -> more suggestion-like

So grammatically it is direct, but pragmatically it can range from instruction to advice.

The Korean specifically includes 만들어서, so it does explicitly say:

• make a separate folder first
• then save them

So save them in a separate folder captures the overall idea, but it leaves out the fact that the speaker is telling you to create that folder.

A more accurate translation would be something like:

• For important documents, create a separate folder and save them there.
• Make a separate folder for important documents and keep them saved there.

So yes, the idea includes separate storage, but the sentence is more explicit than just save them in a separate folder.