email encryption


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I am looking for recommendations for email encryption software. I run a business producing Wills which I want to email to the clients for review before signing. The Will software can produce the documents as pdf's and I want to encrypt the pdf's before sending them. I have looked at symmetric and asymmetric software and for simplicity for the clients, want symmetric: I can send them the password by text message. It seems that to save them having to download extra software I will need to produce self-extracting files that they can open using the password. Problem - the software packages I have trialled produce files with double extensions which my Mcafee package identifies as 'dodgy' and won't send. I use Windows 7 and gmail through Outlook. I wondered if any of you clever people might have any ideas please.