You may want to check out WinPT, which is described as follows . I have not explored this software personally, but its description seems to meet your needs.

1. What is WinPT?

Windows Privacy Tools (WinPT) is a collection of multilingual applications for digital encryption and signing of content. WinPT is GnuPG−based, compatible with OpenPGP compliant software (like PGP) and free for commercial and personal use under the GPL. WinPT helps you protect your privacy. Applications included in WinPT run under the Windows operating system and include:

• GnuPG − an RFC2440 (OpenPGP) compliant application free for personal and commercial use, under the terms of the GPL.
• WinPT−GUI − a traybay application based that uses the Clipboard to let you encrypt, sign, decrypt and verify data; this is performed automatically for you when you select a menu option or via hotkeys. Also includes a key manager and file manager for file security operations;
• WinPT Explorer Extensions − a component that extends the Windows Explorer context menus for files with single/multiple file security and wipe functions;
• WinPT Outlook Express plugin − integration of inline signing, and encrypting/decrypting of email communications;
• WinPT Passphrase Agent − a component to cache passphrases used by GnuPG.
• WinPT cryptographic functionality relies on the GNU Privacy Guard (GnuPG). GnuPG was written by Werner Koch and is GNU Open Source.

The goal of WinPT is to ease installation, integration and use of applications that implement the OpenPGP security standard. This means protecting your data quickly and easily, including but not limited to email, files, instant messaging and in general any data available through the clipboard or through the file system in Windows.