If you are trying to tile a bitmap that wasn't meant to be tiled, you can sometimes use the Transparency tool to feather the edges of your bitmap.  Once the appropriate edges have a transparent gradient applied, you can duplicate that bitmap and position the new duplicated bitmap next to but slightly overlapping the first.  Continue staggering and overlapping your images until you achieve the desired outcome. The end result is a larger image made up of smaller ones, without any noticeable seams.  This only works with some images though.  I might use this technique to extend a photo of the sky or to tile a texture.

Provided by Joe Diaz, CorelDRAW Master, Graphic Designer and Sign Artist.