Adobe says today that it will acquire Macromedia for $3.4 billion, in a move to create a super-platform for rich interactive online content.

Why? Adobe, which makes well-known publishing software (you’ve heard of Acrobat, PDF) seeks to make its online offering more dynamic: “…an industry-defining technology platform” with the combination of its PDF software and Macromedia’s flagship Flash multimedia platform.

It’s the latest in big deals lately. Though federal anti-trust regulators are likely to take a close look, because there are overlapping product lines, according to Alex Slusky, of Vector Capital, who has been active in this part of the tech software merger/buyout world: There’s (1) Macromedia FreeHand and Adobe Illustrator (2) a variety of web design and web publishing tools, and (3) Adobe Graphics Server/SVG Viewer and Macromedia Flash.

More analysis here, via Jeff Clavier.