PDF form is used for for invoice documents. VAT number is included as @@provider_version.tax_ex_number@, but there is no field to enter National ID.
Companies have 2 ID: one of them is a VAT number (this is configured in Tax exemption) and the other is National ID, and it is missing from OBAS.
How to add National ID to Company Profile?
Please use Custom Attributes, the instructions might be found in the SDK guide: