Even if you know what you are doing and really must get some secure document to someone then it is far from straightforward. First you need to get the key. Then you need to get that key onto a computer that you believe is not already compromised. Anything running Windows can be assumed to be less than secure. Whatever happens there will be some hoops to go through to get that key, your secret document and some program to spit out whatever it is you are to send.
Then the fun really starts. You send your message, other party claims it could not be opened. So you go through the hoops again and re-send. At this stage you have probably changed a word or two in your source document. But that does not bother you because you are new to this. You send again. Another reply comes back - 'sorry mate...' - so you send again, probably introducing a few more edits.
Then you never hear back from them ever again. As it turns out you have been man-in-the-middled and those requests for a re-send were purely in the expectation that you would change your message slightly. This provides the 'crib' needed to open your message without knowing the key by our friends in Gloucestershire.
Then the fun really starts. You send your message, other party claims it could not be opened. So you go through the hoops again and re-send. At this stage you have probably changed a word or two in your source document. But that does not bother you because you are new to this. You send again. Another reply comes back - 'sorry mate...' - so you send again, probably introducing a few more edits.
Then you never hear back from them ever again. As it turns out you have been man-in-the-middled and those requests for a re-send were purely in the expectation that you would change your message slightly. This provides the 'crib' needed to open your message without knowing the key by our friends in Gloucestershire.
Where did my tin foil go?