I created a PDF template using LibreOffice version 7.1.3, but unfortunately,
my Orbeon form (built in Form builder - 2018.2.1.201902070135 PE) contains a
handwritten signature field that isn't being shown on the PDF (I tried using
a image controller on LibreOffice, expecting it to be saved as an image).
Is there a way to save the signature in a PDF template, LibreOffice or
Orbeon Forms can insert a handwritten signature in a PDF template, and you
can see this in with the W-9 form on https://demo.orbeon.com (click to open
the form on the link in bottom left of the page, then Review, then PDF). The
field you create for the image is just like any other text field. Orbeon
Forms just uses the Acrobat Form Field to know where you'd like you'd like
to insert the signature, so I don't see a reason why you wouldn't be able to
create it with LibreOffice.
It seems it was indeed capable of using a text field to capture the
signature, I misused the image controller, expecting it to be a generated
image object instead of a text field. Seeing as LibreOffice doesn't have a
Handwritten Signature controller per say, I didn't even think of using a
regular text field.