Turns out it is a font issue:
unicode works, but you have to make sure that the font you are using
includes the characters you want to use. Unlike your operating system,
PDFKit does not do any automatic font substitution.
Source: Reddit Thread comment by /u/devongovett
I tested two fonts that were included with pdfkit. Both 'Helvetica-Bold' and 'Times-Roman' didn't work with the unicode symbols. I noticed in the documentation for fonts that you can add in your own fonts, so I gave the Cardo Font (hosted on Google Fonts) a go as it supports many unicode characters.
Sure enough, it worked. Here is the script I used for testing (Make sure you have the Cardo font available):
var PDFDocument = require('pdfkit');
var doc = new PDFDocument();
doc.registerFont('Cardo', 'Cardo/Cardo-Regular.ttf')
doc.font('Cardo')
.fontSize(20)
.text('Testing [u20AC]', 10, 10);
doc.write('out.pdf');
If you're set on using Helvetica-Bold, download a copy of the font elsewhere (make sure it supports the unicode characters you're after) and register it as I have with the Cardo font.
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