Learn Swedish: Konturen han ritade är väldigt detaljerad. - The outline he drew is very detailed.

The relative pronoun som can be dropped when it acts as the object of the relative clause. In the clause han ritade, han is the subject doing the drawing. Because the outline is the object being drawn, you can omit som. This is called som-bortfall and is very common in everyday Swedish.

If I add a word like inte (not) to the clause han ritade, where does it go since som is missing?

The word order rules for subordinate clauses apply exactly the same way even when som is dropped. The rule is that sentence adverbs like inte must come before the verb. So it would become Konturen han inte ritade är väldigt detaljerad.

Why does detaljerad end in -d here?

Detaljerad is a past participle used as an adjective to describe Konturen. Since en kontur is an en-word and it is singular here, the adjective gets the standard en-word ending -d. If the subject were an ett-word, it would be detaljerat, and if plural, detaljerade.

Could I use tecknade instead of ritade here?