You might have a design with special characters. You can do this in a couple of ways.
Make it an image on the background PDF. In this instance it wouldn't be editable, and any editable text will need to be positioned correctly.
Make it a font character in a label. This way, if the customer doesn't have a facebook account, the icon can disappear.
Make it part of the default content of an editable text field
There are two ways to get the logo into a font. You can use a special font like 'Social Media Circled (.ttf) (that's the one pictured - search for it on the internet). This kind of font has loads of symbols in it and is perfect for the job.
Or. . you can edit an existing font and replace a few characters with the logo of your choice. We have done this a few times using Fontforge. It works quite well, though you have to remember to rename the 'root name' of the font (something like Arial_Custom), and make sure that your character 'glyph' fits into the allotted space, which is different for lower and upper case chars.
