keiyakusyo ha muzukasii kotoba ga ooi si, hitori de yomuno ha sukosi taihen desu.

は marks 契約書 as the topic of the sentence.

So 契約書は means something like:

• As for contracts, ...
• When it comes to contracts, ...

The sentence is then making comments about contracts:

• they contain many difficult words
• reading them alone is a bit hard

This is very common in Japanese: the topic is introduced first, and later parts of the sentence describe it.

In 難しい言葉が多い, the が marks 言葉 as the thing that exists in large quantity.

Literally, this part is close to:

• difficult words are many

Natural English would be:

• there are many difficult words
• it contains many difficult words

Here, 多い often works with が because it describes the amount of something. So 言葉が多い is a very natural pattern.

Compare:

• 人が多い = there are many people
• 問題が多い = there are many problems
• 難しい言葉が多い = there are many difficult words

難しい directly modifies 言葉, just like an adjective before a noun in English.

So:

• 難しい = difficult
• 言葉 = words / language / expressions
• 難しい言葉 = difficult words, difficult language, hard terminology

In this sentence, it probably means difficult wording or hard vocabulary used in a contract.

し is used to give a reason or to list one point among several.

In this sentence:

• 難しい言葉が多いし、
  = there are many difficult words, and... = because there are many difficult words, ...

It often has a nuance like:

• for one thing...
• and also...
• besides...

So the speaker is giving one reason, and then adds another related point:

• there are many difficult words, and
• reading it alone is a little difficult

Sometimes し implies this is not the only reason.

Good question. They are not exactly the same.

• て links actions or states more neutrally.
• そして means and then / and / furthermore in a more explicit way.
• し often feels like giving reasons or listing supporting points.

So here, し fits well because the sentence is not just connecting two facts randomly. It is presenting related reasons why contracts are difficult to deal with.

For example:

• 難しい言葉が多くて、一人で読むのは少し大変です。
  Also possible, but more straightforward.
• 難しい言葉が多いし、一人で読むのは少し大変です。
  Feels more like there are many difficult words, and on top of that, reading it alone is hard.

一人で means alone or by oneself.

Breakdown:

• 一人 = one person / alone
• で = particle that can mark the means, method, or condition in which something is done

So 一人で読む means:

• to read by oneself
• to read alone

The で here tells you the action is done with just one person involved, not with help from someone else.

Here, の turns the verb 読む into something noun-like, so the whole phrase can become the topic of the sentence.

• 読む = to read
• 読むの = reading / the act of reading

Then は marks that whole action as the topic:

• 読むのは少し大変です
  = Reading is a little difficult = As for reading it, it's a little hard

So の is doing nominalization here: it changes a verb phrase into something that can act like a noun.

Yes, 読むことは少し大変です is also grammatically correct.

But there is a slight nuance:

• の often feels a bit more direct, concrete, or natural in everyday speech
• こと can sound a bit more formal, abstract, or general

So:

• 一人で読むのは少し大変です = very natural
• 一人で読むことは少し大変です = also fine, slightly more formal or conceptual

In many everyday sentences like this, の is very common.

Because the phrase 一人で読むの is being treated as the topic.

So the structure is:

• 一人で読むのは = as for reading it alone
• 少し大変です = it is a little difficult

Japanese often uses は after a noun or noun-like phrase to say what the sentence is about. Since 読むの has been turned into a noun-like phrase, it can take は.

Here, 大変 means:

• difficult
• tough
• demanding
• a hassle

So 少し大変です means:

• it's a little difficult
• it's somewhat tough
• it's a bit of a challenge

It does not necessarily mean terrible in this sentence.

大変 can have different uses depending on context:

• 大変です！ = This is awful! / This is serious!
• この仕事は大変です。 = This job is hard.
• 読むのは少し大変です。 = Reading it is a little difficult.

So here it means hard to do, not disastrous.

Yes. 少し means a little or somewhat, and it softens the statement.

Without 少し:

• 一人で読むのは大変です
  = reading it alone is difficult / tough

With 少し:

• 一人で読むのは少し大変です
  = reading it alone is a little difficult

This makes the sentence sound less strong and often more polite or cautious. Japanese frequently uses words like 少し, ちょっと, or 少々 to avoid sounding too blunt.

The implied object is the contract / the contract document.

Japanese often leaves out things that are clear from context. Since the sentence starts with 契約書は, we understand that 読む means:

• read the contract
• read the contract document

So even though 契約書を読む is not stated explicitly, it is understood.

Because the object is omitted.

A more explicit version would be:

• 契約書は難しい言葉が多いし、一人で契約書を読むのは少し大変です。

But repeating 契約書 would sound unnecessary. Japanese often drops objects when they are obvious from context.

So the shorter sentence sounds more natural.

By itself, 契約書 without something like この usually sounds more general:

• contracts
• contract documents

So the sentence suggests a general statement such as:

• contract documents tend to contain difficult language
• reading them alone is a little difficult

If the speaker wanted to point to a specific contract, they might say:

• この契約書は... = this contract document...

です makes the sentence polite.

The plain form would be:

• 契約書は難しい言葉が多いし、一人で読むのは少し大変だ。

With です, it becomes more appropriate for normal conversation, workplace situations, or polite writing:

• ...大変です

Since the sentence is about contracts, a polite tone fits very naturally.