Learn Danish: Bogen findes også i en engelsk version. - The book also exists in an English version.

It looks like a passive verb (meaning 'is found'), but it is actually used here as an active verb meaning 'exists'. Verbs that end in -s but have an active meaning are called deponent verbs. Another common example you might know at this level is synes (to think or seem).

Why is the adverb også placed after the verb instead of before it?

This is a standard main clause, so Danish uses the V2 rule, meaning the conjugated verb findes must be the second piece of information in the sentence. Short adverbs like også are usually placed immediately after the verb in a main clause, unlike in English where 'also' often comes before the verb.

Why doesn't the adjective engelsk have an -e or -t ending here?

Adjectives in Danish must match the gender and number of the noun they describe. Because version is a common gender noun (an en word) and the phrase is singular and indefinite (en engelsk version), the adjective engelsk stays in its basic dictionary form without any extra endings.

Could I use the word udgave instead of version in this sentence?

Yes, udgave is a very common native Danish word meaning 'edition' or 'version'. You will frequently see the phrase findes i en engelsk udgave. Both words work perfectly in this context and both use the preposition i.