Lucia dicit hoc exemplar tam clarum esse quam illud, sed Marcus verba difficiliora in hoc esse putat.

Both verbs introduce an indirect statement in Latin, also called the accusative-and-infinitive construction.

• After dicit: hoc exemplar ... esse
• After putat: verba difficiliora ... esse

So instead of saying Lucia says that this copy is..., Latin says, more literally, Lucia says this copy to be... Likewise, Marcus ... putat means Marcus thinks ... to be...

Because in an indirect statement, Latin normally uses an infinitive instead of a finite verb.

So:

• direct statement: Hoc exemplar tam clarum est quam illud.
• indirect statement after dicit: Lucia dicit hoc exemplar tam clarum esse quam illud.

The same pattern appears in the second half:

• direct statement: Verba difficiliora in hoc sunt.
• indirect statement: Marcus verba difficiliora in hoc esse putat.

It actually is the subject of the infinitive, so it should be accusative in Latin indirect statement. But exemplar is a neuter noun, and neuter nominative and accusative forms are often identical.

So:

• nominative singular: exemplar
• accusative singular: exemplar

The same thing happens with hoc: its neuter nominative and accusative singular look the same. So hoc exemplar here is accusative in function, even though it looks like the nominative.

Tam ... quam means as ... as.

So:

• tam clarum = as clear
• quam illud = as that one

A native English speaker often first learns quam as than, but that is mainly when it follows a comparative, as in clarior quam = clearer than. With tam, it means as.

Because clarum agrees with exemplar, which is neuter singular.

Even though clarum is part of an indirect statement, it still has to match the word it describes in gender and number:

• exemplar = neuter singular
• clarum = neuter singular

Its job here is to act as the predicate adjective in hoc exemplar tam clarum esse.

Illud means that or that one. The noun exemplar is understood and omitted because it would be repetitive.

So quam illud really means:

• quam illud exemplar

English does the same thing: this copy is as clear as that one. We do not have to repeat copy.

Difficiliora agrees with verba.

• verba = neuter plural
• difficiliora = neuter plural comparative adjective

So the phrase means the words [to be] more difficult. In the indirect statement, verba is the subject of esse, and difficiliora is the predicate adjective.

The comparison is understood from the context: Marcus thinks the words in this are more difficult than in that one.

Latin often leaves the second part of a comparison unstated when it is obvious. So verba difficiliora in hoc esse means something like the words are harder in this one, with the comparison to the other exemplar implied.

If Latin wanted to state it explicitly, it might say something like quam in illo.

Because in with the ablative expresses location: in this or in this one.

Here hoc is ablative singular, and the noun exemplar is again understood:

• in hoc = in this [exemplar]

This is different from hoc exemplar earlier in the sentence, where hoc is part of the accusative subject of the infinitive. The form hoc happens to be the same in both places, even though the case is different.

Latin word order is much freer than English word order because Latin endings show the grammatical relationships.

A few things are especially normal here:

• esse often comes near the end of its clause
• important words can be placed early for emphasis
• sed neatly marks the contrast between Lucia's opinion and Marcus's opinion

So the sentence is not random; it is idiomatic Latin word order.

Yes. The sentence is built very neatly:

• Lucia dicit
  • indirect statement
• sed Marcus ... putat
  • indirect statement

First half:

• hoc exemplar tam clarum esse quam illud

Second half:

• verba difficiliora in hoc esse

That parallel structure helps show the contrast: Lucia comments on the overall clarity of the exemplar, while Marcus comments specifically on the difficulty of the words in it.

Yes. Latin demonstratives like hic, haec, hoc and ille, illa, illud can work in two ways:

• as adjectives: modifying a noun
  
  • hoc exemplar = this exemplar
• as pronouns: standing on their own
  
  • illud = that one
  • in hoc = in this one

That is exactly what happens in this sentence: hoc first modifies exemplar, while illud and later hoc stand without the noun because it is understood.