What does the "pen tool" primarily allow a designer to do?

The pen tool is a fundamental feature in graphic design software, specifically designed for creating custom shapes and paths. It provides designers with the ability to draw precise lines and curves by defining anchor points and control handles. This versatility allows for the construction of intricate designs that can be manipulated easily, making it an essential tool for vector graphics.

Using the pen tool, a designer can create complex shapes that are not limited to geometric forms, enabling them to craft unique illustrations or logos. The paths created with the pen tool can be filled, stroked, or used as masks, adding to the range of creative possibilities.

While gradients, raster image editing, and filters are important aspects of graphic design, they are not functionalities offered by the pen tool. Gradients involve color transitions, raster image editing deals with pixel-based graphics, and filters apply effects to images, all of which require different tools and techniques beyond the capabilities of the pen tool.