Przeczytanie tego raportu było trudne.

Przeczytanie is a verbal noun: a noun made from a verb.

It comes from the verb przeczytać = to read through / to finish reading.

So przeczytanie means something like:

• the reading of
• the act of reading through
• finishing reading

In Polish, these forms behave grammatically like nouns, even though they are built from verbs.

This is about aspect, which is very important in Polish verbs.

• czytać = imperfective = to read, focusing on the process, habit, or ongoing action
• przeczytać = perfective = to read through / read completely

So:

• czytanie tego raportu = reading this report, focusing more on the activity/process
• przeczytanie tego raportu = reading this report completely / finishing it, focusing on the completed act

In this sentence, przeczytanie suggests that getting through the whole report was difficult.

Because after a verbal noun like przeczytanie, the thing being acted on is usually put in the genitive case.

So:

• verb: przeczytać ten raport = to read this report
• verbal noun: przeczytanie tego raportu = the reading of this report

This is a very common pattern in Polish:

• napisać list → napisanie listu
• zrobić obiad → zrobienie obiadu
• przeczytać raport → przeczytanie raportu / tego raportu

So the accusative object of the verb often becomes genitive after the noun form.

Both are in the genitive singular.

• ten → tego
• raport → raportu

That is because they depend on the verbal noun przeczytanie.

Because przeczytanie is grammatically a neuter singular noun.

In the past tense, być agrees with the subject:

• masculine singular: był
• feminine singular: była
• neuter singular: było

Since the subject is przeczytanie, we get:

• Przeczytanie tego raportu było trudne.

Because trudne agrees with przeczytanie, which is neuter singular.

So the adjective must also be neuter singular:

• masculine: trudny
• feminine: trudna
• neuter: trudne

Here, trudne is part of the predicate: was difficult.

Yes, absolutely. That is a very natural alternative.

Compare:

• Przeczytanie tego raportu było trudne.
• Trudno było przeczytać ten raport.

The meaning is very similar, but the style is a bit different:

• Przeczytanie tego raportu było trudne sounds a little more nominal and slightly more formal/written
• Trudno było przeczytać ten raport sounds more everyday and more directly verbal

So the original sentence is correct and natural, but it is a bit more formal in tone.

No, Polish word order is fairly flexible.

The neutral order here is:

• Przeczytanie tego raportu było trudne.

But other orders are possible, for example:

• Trudne było przeczytanie tego raportu.
• Tego raportu przeczytanie było trudne. (possible, but less natural in ordinary speech)

The original version is the most standard and natural.

Usually yes, because it comes from the perfective verb przeczytać.

That means it points to a completed whole event: reading the report through to the end.

If you wanted to focus more on the process itself rather than completion, czytanie would be more likely.

So this sentence does not just mean that being in the middle of reading was difficult; it suggests that getting through the report was difficult.

Yes. Raport is a masculine inanimate noun.

Its singular forms include:

• nominative: raport
• accusative: raport
• genitive: raportu

That is why in this sentence you see raportu.

Yes, that is a very good way to think about it.

The whole phrase:

• przeczytanie tego raportu

functions as the subject of the sentence.

Then the rest says something about that subject:

• było trudne = was difficult

So structurally, it works like:

• This task was difficult
• Reading this report was difficult

In Polish, the subject just happens to be a verbal noun phrase rather than an ordinary noun.