While the Excel Software DRM tools may be a good security system -- there are a few things you should be aware of.
The company lists over 50 security packages so you'll need to really pay attention to what packages are available and which ones will suit your purpose best. There are selections for the Mac, Windows or both. It's unclear if these are installation packages or distribution packages.
For example - If you purchase a Windows package (for you Windows Computer) can you protect/distribute PDF files to both Mac and Windows customers?
The base price for DocProtect for Windows is $495 but it appears that only provides a security "wrapper" for your PDF file. QuickLicense appears to be a licensing option that you also need to add to your product. Base cost $595 for the Windows version.
Then to make the complete DRM functional you also need to Sign up for something called Safe Activation. This is an online service that costs from $40 to $160 per month. For the Starter package ($40) you can have 4 products and 1000 Customers/Serial Numbers. (Instead of the monthly Safe Activation account -- you can purchase WebActivation for a one time cost of $2500).
Therefore it appears to me that it will cost you over $1000 initially plus a minimum of $40 per month -- just to get started.
You asked for recommendations -- so you might be interested in the HYPrLock PDF security system. With HYPrLock you can distribute/protect unlimited PDF files for a one time purchase of just $145.00
Unlike the Excel Software system, HYPrLock is simple to setup and easy to use. With HYPrLock, PDF files are hardware locked to one customer/computer and customer/clients will appreciate HYPrLock's instant one time activation. While HYPrLock can only be used on a PC you can distribute PDF files to Mac customers who have Windows emulator software.
HYPrLock provides military standard (****
er proof) PDF security that prevents copying, sharing or editing. You own and control everything so there are no hidden fees or monthly service charges.