This article is primarily written for SCORE volunteers who want to email PDF documents from the Handout Library to clients, but of course it applies to anybody who wants to attach a PDF document that is stored on G Drive to an email.
If you have tried to email PDFs documents as attachments directly from the G Drive using your computer browser, you know that is a real pain-in-the-you-know-what, and in fact cannot be done without jumping through some serious hoops.
From your browser, Google makes it easy to share documents, but I really want to discourage this use for distributing PDFs to the public. When you Share a document, you are permanently adding a permission for somebody else to work with the file. If you're not careful, you might give the permissions to change or delete the file for example. So, please, Do not Share documents with the public. Email PDFs as attachments instead - here's how.
If you have an organizational account (@scorevolunteer.org or @nuevassonrisas.org), the easiest way to attach a document from the G Drive to an email that you're writing on your computer is to use Drive File Streaming. Please read the article G Drive File Streaming and install it. You can than attach the PDFs from the G: drive on your computer as you are used to doing. This is yet another excellent reason to get your organizational account - see Branded Nuevas Sonrisas Email article (at SCORE, you already have one).
If you don't have Drive File Streaming installed, the only way to accomplish attaching a PDF to an email on your computer is to download the file first explicitly, but of course that (1) gets old really quickly and (2) you never know whether you have the latest version of the PDF. I strongly discourage you from using this method.
Finally, it turns out that it is easy to attach PDFs files to an email on your smartphone. Find the PDF in the Drive App (see G Drive Mobile Navigation), touch the 3-dot icon to the right of the file, swipe up the menu to reveal more options, and touch "Send a copy." You'll be given a chance to use any one of several methods to send it - Mail, Message, and whatever else you might have set up your iPhone to do. Caveat: if you have not done this before on the smartphone, the file must be downloaded first before it can be emailed, and this may take some time especially for large files.