TFG

This has turned out to be a really useful tip for the work I'm doing. Thank you for pointing it out!

When applied to a single vector object, ‘Add’ performs a Boolean add of that object to itself. As with all Boolean operations in the Affinity apps, the resultant object is unrotated.

@Return - That works nicely. Many thanks for the tip. Not quite sure why "Add" would do that, but I'll take it.

Geometry> add is an option.
 

When I import vectors from my CAD in Designer, I'm occasionally seeing odd behaviour in the way that it parameterises what are simple shapes (rectangles with rounded corners). Sometimes I'm seeing this, which is what I'd expect:

...but for another, similar, shape, I see this:

 
It doesn't seem to affect how the shapes edit, but the Transform tab obviously reports meaningless dimensions. I need to be able to check that these shapes are the correct size, so that's causing me a problem.
Is there anything that can be done to 'reparameterise' the fit of the grips for these shapes, without altering them? I'm not sure what is causing some to behave correctly and others not.

Press the period key to switch the object's bounding box to "regular bounds" (which is a tight rectangle aligned with the document's X and Y axes), then inspect the Transform panel.

In the Keyboard Shortcuts screen, where it normally says "File" (top left), change that drop-down to the "Miscellaneous" option

Because the part of the file that is to be printed has to be converted to vectors. It's company policy, to avoid discrepancies in the reading of fonts at suppliers, which we've ha bad experiences with in the past. The job(s) could go out to any number of suppliers, all with different setups. We don't have control over that.