Update: With AutoCAD 2016 and later versions the feature of password protecting AutoCAD files has been disabled because it no longer meets the present security standards. You can open password protected files of older versions using AutoCAD 2016 or any latest version without requiring passwords. For more on this see this page on Autodesk knowledge network.
However, you can use some alternative methods for password protecting files like protecting files using Network permissions, Autodesk 360 or other third party tools. In this article, I have explained password protecting files using WinRAR.
Download WinRAR from this page and install it on your PC. Right click on drawing or select multiple drawings then right click and select add to archive from the contextual menu. Archive name and parameters window will pop up, select general tab and click on set password button as shown in the image below.
Choose a password and click on OK to close all open windows. You now have drawings in password protected archives.
You can also share files to users without allowing them to copy or modify it in any way using A360 cloud file sharing. To share the read-only drawings upload it on your A360 account and select the share option as shown in the image below.
From share dialogue box select the options as per your requirement like allowing downloads or password protecting drawing link. You can then share this link to users who can view the drawings using their browsers. The recipient can view the drawings and measure different geometric features from the web browser but can’t modify it.
There are also other methods like encrypting CAD files using third party encryption software but most of them are paid or available as a trial with limited features.
If you have questions related to this tip let me know in the comments below.