Janome has Acudesign which allows you to import embroidery designs from other sources and modify them. So your best path to success is Embrilliance which will allow you to purchase files from iBroidery, make adjustments, and then save it out to your Brother embroidery machine. While Brother does have its own software, many people have difficulties getting it to work well. You may want to be more experienced with designing for an embroidery machine before you buy this. You can merge in existing designs with your lettering.
Some users felt that the PDF version of the manual that was provided was difficult to read. Amazing Designs offers a day free trial which is a great way to learn the software before you buy it. Having said that, if you're beginner you may not need to invest in and editing software when you're starting out. Note: It's not an editing software, so don't expect to edit your designs with it. So you can download and test it all out with your embroidery machine before you buy the software. If your embroidery machine has a Flash drive port, you can easily create designs using another program, and download to your embroidery machine using a USB stick drive. For the price, you may want to skip this one. Be sure to use the right size designs for your machine otherwise machine will reject the card. I do appreciate the programs that let you test out the interface. Plus it saves out designs that are usable on all USB sported machines as well as can be installed on Windows and Mac. It's the most robust package available and is being sold at an affordable price point.
It can read and write many embroidery design formats. More on this later! In the battle for the best software for embroidery machines, I've compared the four major competitors. For those of you looking for the digitizing software, you can find the best digitizing programs here.