In your regex you have a specific name used as a anchor, for example “invoice number:” If the specific is available in the document, it will extract the values, otherwise it won’t.
In such case, we have provided all possible issues with “|” this separation, which means “OR” in regex.
(?<=Tax Invoice No : )(\d+)|(?<=Tax Invoice no : )(\d+)|(?<=Tax Invoice Number : )(\d+)
