https://settlers.jakelee.co.uk
I noticed the only online copy of this manual was a broken old Tripod site, so wanted to ensure it could be easily accessed properly. Most of this manual is from the History Edition, with /tips/ from the Ultimate Edition.
I had to make quite a few fixes to get this online (encoding, filenames, multiple editions etc), if you're interested in reading about them: https://blog.jakelee.co.uk/settlers-3-online-manual/
If you spot any broken links etc please raise an issue, tweet, or email me, thank you!