Bildefilen lagres i dette filformatet.

Because Norwegian, like German, very often makes compound nouns by joining words together.

• bilde = image, picture
• fil = file
• bildefil = image file
• bildefilen = the image file

So bildefilen is not two separate words. It is one compound noun plus the definite ending.

The ending -en makes the noun definite singular.

• en bildefil = an image file
• bildefilen = the image file

In Norwegian, the definite article is often attached to the end of the noun instead of being a separate word like the in English.

Lagres is the present passive form of the verb å lagre = to save, to store.

• lagrer = saves / is saving
• lagres = is saved / gets saved / is being saved

The -s ending is a common way to make the passive in Norwegian.

So:

• Bildefilen lagres = The image file is saved / is being saved

Not exactly, although both can often be translated with passive English.

• lagres = is being saved / gets saved / is saved
  This often focuses on the process, routine, or general action.
• er lagret = is saved / has been saved
  This often focuses more on the result or completed state.

So in many contexts both are possible, but they are not always interchangeable.

Because filformat is a neuter noun.

In Norwegian demonstratives agree with the gender of the noun:

• denne for common gender singular
• dette for neuter singular
• disse for plural

Since it is:

• et filformat = a file format

the correct form is:

• dette filformatet = this file format

Because after a demonstrative like denne, dette, or disse, Norwegian normally uses the noun in the definite form.

So:

• et filformat = a file format
• filformatet = the file format
• dette filformatet = this file format

This can feel strange to English speakers, because English uses only this file format, not something like this the file format. But in Norwegian, this pattern is normal.

The ending -et marks definite singular neuter.

• et filformat = a file format
• filformatet = the file format

Since filformat is a neuter noun, its definite ending is -et.

Here i means in.

So:

• i dette filformatet = in this file format

This phrase tells us the format in which the image file is saved.

English and Norwegian often match here:

• saved in this format
• lagres i dette filformatet

This is normal Norwegian main-clause word order:

• Bildefilen = subject
• lagres = verb
• i dette filformatet = adverbial phrase

So the basic structure is:

subject + verb + other information

That is why the verb comes in second position in the sentence.

Yes. You could say:

I dette filformatet lagres bildefilen.

That is also grammatical, but it changes the emphasis. Starting with I dette filformatet puts more focus on the file format.

Notice that when a different element comes first in a main clause, the verb still stays in the second position:

• Bildefilen lagres i dette filformatet.
• I dette filformatet lagres bildefilen.

It can mean any of those, depending on context.

The Norwegian present passive lagres is quite flexible. It can describe:

• a general fact
• a routine action
• an action happening now
• a technical instruction or system behavior

So in context, Bildefilen lagres i dette filformatet might mean:

• The image file is saved in this file format.
• The image file is being saved in this file format.
• The image file gets saved in this file format.

English chooses among these more explicitly than Norwegian sometimes does.

Yes.

• bildefil = bilde
  • fil
• filformat = fil
  • format

Compound nouns are extremely common in Norwegian. The last part usually tells you the basic category:

• a bildefil is a kind of fil
• a filformat is a kind of format

This is a very useful pattern to notice as you learn vocabulary.

One possible indefinite version would be:

En bildefil lagres i et filformat.

That means something like An image file is saved in a file format, though in natural English that sentence is less specific and may sound odd without more context.

Compare:

• Bildefilen lagres i dette filformatet. = The image file is saved in this file format.
• En bildefil lagres i et filformat. = An image file is saved in a file format.

This helps show how Norwegian marks definiteness with endings and articles.