Completely impossible to answer your question directly since the scripts are incomplete and missing critical information.
For example:
tell newDoc
export to pdfPath as PDF
end tell
Depends a lot on what newDoc is (presumably a reference to a newly created document, but there's nothing to confirm/deny that. It also depends on what 'pdfPath' is - Numbers requires POSIX-style paths, but we can't see what your pdfPath is.
I can tell you this code works, but can't tell you how it relates to your code:
tell application "Numbers"
set newDoc to make new document
tell newDoc
export as PDF to (POSIX path of (path to desktop) & "my.pdf")
end tell
end tell
Likewise:
set thisImage to make new image with properties {file:imagePath, width:100}
depends on a) what imagePath is, and b) where you're targeting this.
Images are elements of sheets, not documents, therefore this needs to target a sheet in the current document. Are you doing that?
Here's an example showing it working, based off my earlier script:
set myfile to choose file of type "public.image"
tell application "Numbers"
set newDoc to make new document
tell newDoc
tell sheet 1 to set thisImage to make new image with properties {file:myfile, width:100}
export as PDF to (POSIX path of (path to desktop) & "my.pdf")
end tell
end tell
Note how the image targets a sheet, not the document.
