So let me try to explain why being able to cut and paste is necessary from a sales perspective.
Lets say you have a doc that is five pages long, and filled with a lot of tech jargon.
You are reaching out to a decision maker that is not a tech guy, but a money guy that just wants to know what you bring in simple terms to help their entire organization make/save money. It is much better to be able to cut and paste the pertinent info from the originating document to that money guy directly into the body of the email so that he sees that information and acts upon that information. I don't need to tell him all about everything that we do to prevent cyber attacks, I only need to give the contact a slight sampling of what we are able to provide that will prevent attacks and save their firm money and protect their reputation. (Also, This person will not open an attachment because he has heard that he should not open attachments.) The client money person does not want to go through a multi-page doc from me describing in detail what we do to prevent account takeover.
This is just one small scenario among hundreds of scenarios, that tell you why I need to be able to cut and paste into the body of the email rather than attaching the entire tech document. Some of the target people at the client prospect will not even touch an attached document.