First off, the Create Magic Scroll spell on page 211 of PFRPG 2nd Ed is basically the same as the Rifts: Book of Magic version.
However, the line I was remembering
does still exist in the Alchemist section of the book, on page 247:
The moment the scroll is read, the magic is activated and the spell is cast. The PPE necessary to cast the spell scroll is magically implanted and stored in the written words. Thus, as the scroll is read, the words vanish and the spell is cast. If the reader stops at any point for more than three seconds, the spell is ruined and the writing on the scroll vanishes without casting its magic.
Only the name of the spell will remain after a reading, so it is safe to only read the heading on a scroll; not unraveling it beyond that point to avoid accidentally glancing at the magic words and reading them.
This indicates that so much as seeing and recognizing a single letter or word of the spell on the scroll triggers it. At that point, you MUST cast the spell, or lose it forever.
However, I suspect that at least part of this is a holdover from 1st Edition, because the section on scrolls opens with:
The alchemist is one of the few people in the world who can turn a spell invocation into a magic scroll.
Since any Wizard and some Witches can gain access to the Create Magic Scroll spell, the "few people in the world" claim seems dubious. And since the Create Magic Scroll directly contradicts the description in the Alchemist section ("must be read aloud" vs the ability to trigger a scroll just by glancing at a single word), a GM has to select one to accept as canon, and disregard the other. Since every version of CMS is basically the same (including in newer sources), and the Alchemist only exists in PFRPG, I'm going to have to agree with drewkitty - the scroll must be read aloud.