When using prime symbol in product name or its attributes descriptions/values, it is replaced with a question mark in PDF (invoices, etc...). Prime symbol is part of Unicode, and is used to describe feet or minute value.
Prime symbol is replaced in TCPDF::UTF8ToLatin1. TCPDF check if this symbol exists in Unicode by searching it in TCPDF_UNICODE_DATA::uni_utf8tolatin.
TCPDF seems to be deprecated and replaced by tc-lib-pdf.