If you are looking for a straighten tool in Perfect Photo Suite it could prove frustrating because it is called levelling and only shows up when you select the cropping tool, either under perfect layers, perfect enhance, perfect resize. Once you select the crop tool from the left hand tool bar, a levelling tool shows up un the middle of the tool bar above the image, You can either enter a rotation angle, or click on the small triangle to get an interactive slide that will tilt the image or better still click on the little bubble level icon and the cursor will change into the level tool. Move to one convenient place on the strong horizontal (such as the horizon) and click and drag a line across your photo that want to be level (ie the other side of the horizon) then click again.
When you release the mouse the photo will be adjusted by the desired angle. The cropping marks will automatically be adjusted to the best fit cropping of the rotated image to avoid blank edges. All very simple once you find it.
There is also a rotation tool in the layer transform tool within Perfect Layers which allows both the speciation of the angle and the interactive slider but it does not display the levelling tool.