Hello sir, How are you ?
I have read your project requirements regarding
1) Currently, you have a form using google sheet, Which you need to convert to custom form on your website
2) The data which user is filling should be converted to pdf and then send through the mail
3) You need to create a google calendar event from the data which the user is filling.
4) Finally, everything you need in WordPress.
Let me clear this, I have worked with all of these API like google sheet API, Google Calendar API, and know exactly how to work on it.
About the PDF part, I will use the PHP PDF library which is open-source.
So I can say that I can complete all of your requirements by creating a custom plugin.
Let's discuss this more through chat and start working on it.