Self decryption file/folder software

I have a need to forward confidential file/folders to clients. I use OS X SL and my clients use (I guess) Windows (various flavours). Unfortunately some of my clients use workstations and cannot/not authorised to install decryption software on their machines.
Question:
Is there any software available whereby I could encrypt my file/folder which would self decrypt on my clients' Windows Platform with just the password. No additional software is required at the other end.

I have tried Meo which worked once. All subsequent encrypted files failed to open on their own. Don't know why.

Files to be encrypted are generally .doc, .xls and .pdf.

I can't think of any piece of software but you can password protect Office documents. In Word and Excel, go to Word/Excel > Preferences > Security. I'm not sure if the Windows user will require Office 2007 but it's worth a shot. As for the PDF, go to File > Save As... and at the bottom will be the option to encrypt your PDF. As before with Word and Excel, I'm not sure what software will be required to decrypt it (never done this) but it might work with Adobe Reader which I assume they have installed.

Take one step back and ask yourself what you want to protect yourself against ....
Do you want to protect the information whilst it is traveling over the internet, or do you want to protect your information from being disclosed once it arrived at its destination .... or both.

There are different solutions for different scenario's and you will have to balance risk against useability.
The only way to 100% safely deliver information is for you to deliver it in person and that is not pragmatic ( I assume )

Cheers ... McBie

The sole reason for encrypting the file/folder is not to fall foul of the Data Protection Act in the UK. The data goes to overseas clients who generally are Windows based. I am in the midst of converting to a paperless system and therefore pdf is the main format, with xls a close second.

I am not sure if this is the most elegant solution, but you could always add the files to a .zip or .rar archive, which you can protect with a password. You can even encrypt filenames etcetera, if I am correct.

For Mac, I think StuffIt is one of the few that allows encryption when creating .zips, though. And unfortunately, StuffIt is not free. But perhaps you can find a free alternative to WinZip?

I do have an older Stuffit Deluxe (Windows) and have experimented with encryption when creating zips. This is the best option available at the moment though I have to do the encryption on the VMware Fusion Windows first. Need to look at the Stuffit Mac Version first before committing to a purchase.
Thanks Kaham..... forgot about Stuffit!

I now have the Stuffit Deluxe 2010 Mac version and am very pleased with it. With a little setting work, I now have the software which satisfies my requirements.