The same issue I have faced in my project. unfortunately, there is no inbuilt VBO in BP to deal with pdf. the method you are using may compress the content of pdf.
I have built my own custom object for this purpose, you can use it
Just place Microsoft.Office.Interop.Word.dll to Blue Prism Automate folder
Thanks
------------------------------
Aqib iqbal khan
Junior QA Associate
SQS
Asia/Kolkata
------------------------------