Hello, guys.
I work for a 6 years in software development. I see your tasks and it is pretty clear for me))
You have to work with pdf files, send emails, work with web services and work with excel sheets. I think we're done here, your choice should a C#/.NET.
It has few libraries such as PDF extract for PDF, i've used it, it works ok.
It has [login to view URL] namespace for working with emails. i used it. it's ok.
Saving documents - it's obvious in .net, every student do it in school. i did it. million times. it's ok.
And the last part - EXCEL documents. You should use [login to view URL] .net library. I used something like that a year ago. unfortunately i don't remember the library exact name now but it was ok.
Also i've created an excel file just with a stream in c# and it also didn't make any problems for me. It was just ok.
I hope i have explained why .net is the most matching platform in your situation.
You welcome.
Victor))