Client filled in form and sent it back to me, it needs my signature now but I can't edit it anymore

I've made a fillable application form, sent it to my client. My client filled it in and sent it back to me, but this form now needs to be signed by me (I'm approving the form) but I can't edit it anymore, fillable fields are gone now? is it because my client protected this file? it has all of my clients info, just won't let me sign it and approve it