HERE and open them in a picture editing software that allows you to add text. My favorite and easy to use program is Google's free Picasa program. Once you add your text and save as a jpeg file, you can send to your favorite print shop (mine is Costco, lustre finish). I personally use a wholesale postcard printing service (like Overnight Prints) which not only gives you a nice sturdy card stock, but also allows you to add details for the invitation on the back and can usually be ordered with envelopes! Oh- and is super cheap... but will take longer to get through the snail mail!
Let me know if you are able to use these for your baby shower- I would love to see!! Also, any questions, just let me know! Enjoy and happy showering :)
PS: Many of these design elements and fonts are free to use for those of us amateurs who are not making things like these for money!! I would like to thank just a few of these awesome places for having free goodies!!
Kimberly Geswein Fonts
The Coffee Shop Blog