You might find out that pen strokes are thicker / thinner on a page than on another despite the same thickness value (e.g. 2.0 mm) and zoom level:
This is simply because one page is much larger in page size than the other (e.g. A3 vs A5).
As pen thicknesses are based on the GoodNotes Standard size (closer to the US Letter size), the same pen thickness will look thinner on the larger pages.
If you would write with a pen tip that has a thickness of 1 mm on a piece of real paper, it would leave a line of 1 mm thickness. Now, this is where it is getting tricky and we have to consider the iPad size you're using. GoodNotes will always show the full page by default, no matter if you're using a very large A3 page or a much smaller A5 paper. The two pages technically look similar on your iPad screen because your device size won't shrink or grow depending on the displayed paper. Thus, the thickness you selected will be relative to the paper size. A 1mm line will look much thinner on an A3 paper than on an A5 paper on the same device.
If you have a Mac, you can resize the PDF thus:
- Open the PDF in Mac Preview and press command+P.
- Choose a paper size, say, "US Letter" and select "Save as PDF" from the lower-left list:
Then import the result PDF to GoodNotes and the issue should be gone.
If you don't have a Mac, you can use an online service to resize your PDF.