The actual recular expression would be this:
into #(\w*?)( |$)
Make sure you use RegexOptions values so that the "into" will match "INTO" and so that the $ will match the end of a line.
The expression you created will find the INTO statement whether it is on a line by itsself or on one line with the rest of the SQL statement?
There is really no such thing as a "brief" explanation when it comes to RegEx.
As for finding the INTO if it's on it's own line, no, you'll need to replace the first " " with a ( |$) or something like that.
\binto\b.*?#(\w*)\b
However, use RegexOptions.SingleLine instead of MultiLine.