Issue when printing or saving a form containing non latin characters

[calixteman]

Attach (recommended) or Link to PDF file here:
https://www.nta.go.jp/taxes/tetsuzuki/shinsei/annai/joyaku/annai/pdf2/250.pdf

Configuration:

• Web browser and its version: Firefox 81.0a1
• Operating system and its version: Debian 5.6.7-1
• PDF.js version: latest in Firefox nightly
• Is a browser extension: No

Steps to reproduce the problem:

1. Open the pdf and paste the following text "本 店 又 は 主 た る 事 務 所 の 所 在 地" in "Full name" and in "Domicile and residence" textfields
2. Print or Save the pdf

What is the expected behavior? (add screenshot)

What went wrong? (add screenshot)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

[calixteman]

FYI, I'm fixing it and I should have a patch quickly, so @timvandermeij you can assign it to me, thanks.