hello alex, in most cases, it requires a pdf editing app, and not simply a pdf viewing app. with a pdf editor, you could add an image of your signature, if you made a jpg of it, into the pdf. then resize it and place it the image in the right spot on the pdf. the other way is to convert the pdf into an editable document, such as a MS Word document. And again you could add an image file that had your sig, then resize the image and place into the right spot. Afterwards re-convert that document back into a pdf. There is also a form of electronic / digital signatures where as an actual image of your sig is not necessary. but i dont use this method. Lastly, you could prit the pdf on a printer, sign it with a pen, then rescan it back into your system as a pdf.