Whatsapp automation

I need to send pdf file automatically to my client as per his number in WhatsApp

I have all my data in Google drive and store path in Google sheet.
Let's say A for 1.pdf
B for 2.pdf and C for 3.pdf
If Mr a require for his invoice pdf send me msg Invoice than whatsapp should send 1.pdf to him
Same like If Mr B require for his invoice pdf send me msg Invoice than whatsapp should send 2.pdf to him