ImageMagick only kicks in for Gallery forums.
Attached files to regular posts are never touched by ImageMagick. They are attached exactly as the uploader uploaded them as; whether the attachment be a pdf, zip archive, or image file.
---
Gallery forums limit attachments by file size, image dimensions, and only allow images (gif, jpg...etc)
Regular forums only limit attachments by file size and type (gif, jpg, pdf, zip/rar, txt...etc)
