If you haven't used the PCB Footprint wizard (which will place pads on the exact pitch you specify), you can add pads using the Type Coordinate or Add Multiple pads items from the right mouse context menu when actually adding pads in the Footprint editor.

You can also place pads manually onto the grid points. If you need to specify a grid of an equal spacing, set the grid as required in the Grids dialog on the Settings menu.

You can also use the Add Multiple and Replicate commands to produce repeated patterns of pads (as well as other items).