Learn Hardcore Japanese: kono siryou ha mozi dake de naku syasin mo ooi. - These materials have not only text but also lots of photos.

だけでなく means “not only … (but also …).” It’s a set pattern: X だけでなく、Y も …
The で here is not the location/means particle; it’s the 連用形 (continuative form) of the copula だ in the negative でない. So でない → でなく (conjunctive).
You’ll also see だけではなく (with は), which adds emphasis to “not only X” and is a bit more explicit. Casual speech often uses だけじゃなく.

Why is 写真 followed by も instead of が or は?

In the pattern X だけでなく、Y も …, Y typically takes も to mean “also/as well,” balancing with the “not only X.”
If you use が (写真が多い), you simply state the fact “there are many photos,” but you lose the clear “also” pairing with X.
は after 写真 would sound contrastive (“as for photos…”) and is not the default in this construction.

Is 写真が多い also correct? How does it differ from 写真も多い?

Yes, 写真が多い is fully grammatical: この資料は文字だけでなく、写真が多い。
Nuance:
- 写真も多い explicitly signals addition: “not only text; there are also many photos.”
- 写真が多い just states the property; the “also” idea is weaker/implicit.

Why doesn’t the sentence end with です? Is that rude?

多い is an i-adjective and doesn’t require a copula. Plain style ends with 多い.
Polite style adds です: この資料は文字だけでなく、写真も多いです.
Never say 多いだ—i-adjectives don’t take だ. Polite question: 多いですか？ is fine.

What exactly does 文字 mean here? Why not 文章 or 文?

文字: individual characters/letters; by extension “text” as opposed to images. Perfect when contrasting text vs. pictures.
文章: prose/composition; the writing as a whole.
文: a sentence.
テキスト: “text” (loanword), or “textbook” depending on context. Here, 文字 is the natural choice.

What does 資料 mean, and how is it different from 書類 or 文書?

資料: materials/data/reference handouts—things used as sources of information (slides, handouts, reference packets).
書類: paperwork/forms/documents you fill in or submit.
文書: written documents/texts (letters, memos, official writings). Depending on context, 英語 “document” might map to any of these, but for a handout or set of materials, 資料 is spot on.

Can だけでなく attach to verbs and adjectives too, or only nouns?

It works with all major parts of speech:

Noun: 日本人だけでなく、外国人も参加します。
i-adjective: 安いだけでなく、質もいいです。
na-adjective: 静かなだけでなく、便利です。
Verb (dictionary form): 読むだけでなく、書くことも大切です。

Why is は used after 資料?

は marks the topic: “As for this handout…”
It frames what follows (文字だけでなく、写真も多い) as a property of that topic.
Using が after この資料 would present it as new/unknown information; は is more natural when describing a known item’s features.

Is there any difference between だけでなく and だけではなく?

Both are correct. だけではなく (with は) puts a bit more focus on “it’s not the case that it’s only X,” so it can feel slightly more emphatic or careful. In practice, they’re often interchangeable.

Why use 多い instead of たくさん?

多い is an adjective meaning “many,” and it typically takes a subject with が: 写真が多い.
たくさん is an adverb/quantifier; you pair it with a verb like ある: 写真がたくさんあります.
Alternatives:
- この資料は写真が多い。
- この資料には写真がたくさんあります。
- 写真が多く載っています (“many photos are included/printed”).

Does 多い apply to both 文字 and 写真 here?

No. In この資料は文字だけでなく写真も多い, the adjective 多い directly describes 写真. The sentence says the document doesn’t only have text; it also has many photos. It does not claim there are “many characters/text” as well.

Are there more formal or stronger alternatives to だけでなく?

〜のみならず: very formal/literary. この資料は文字のみならず、写真も多い。
〜ばかりでなく: “not just,” often a bit stronger or with a complaining nuance in some contexts. この資料は文字ばかりでなく、写真も多い。 Use だけでなく for neutral, all-purpose style.