Here’s what the Flux documentation says about creating and modifying PCB board outlines:

"In this tutorial, we'll explore the different ways to create and modify board outlines in Flux, allowing you to customize your PCB shape and size to fit your project requirements.

The board outline defines the physical boundaries of your PCB and is one of the first design decisions you'll make. Flux provides several options for creating board outlines, from simple shapes to complex custom designs.

We'll cover the following topics:

Flux has built-in support for simple shapes (circular and rectangular). For complex shapes, please refer to the section on Advanced (custom) shapes.

This is the PCB board outline: the closed shape that defines the physical edge and overall size of your finished circuit board.

For example, setting it to 100 mm × 80 mm creates a rectangular PCB of those dimensions. Components, copper, and holes are placed within it; the manufacturer cuts the board along this boundary.

In Flux, open the PCB Layout, select the board/background, then edit the board’s width, height, and shape in the properties panel. The PDF you uploaded is separate—it appears to be a BOM/assembly document, not a PCB-outline drawing.