I tried a lot for the steps as you mention. But for pdf, selector is not working for Get text activity. Actually the selector is getting static so its only working for any one pdf by using Acrobat Reader. No such tags are getting in the UI Explorer which will make it dynamic.
Even if you do it by OCR atlast you will have to use regex only to extract the Invoice No.
So its best to do by using Read PDF Activity.
One thing can be happen that Just to show the Invoice is opening in PDF you can do it to show by using Start Process Activity but atlast search the invoiceNo can be done by using the method that i have already implemented.
Hope this may help to solve your query
Definetly mark as solution & like it.
Er Pratik Wavhal