Suggest to use online tool: https://dochub.com
After register account on the dochub, you can upload pdf files and start to edit signature.
There is a button "Sign" , you can create your signature when you use dochub at first time as below:
You can draw your signature on PC:
You can see the signature picture in the menu "Sign" after you save your signature on last step.
You can add the signature picture into your pdf file and edit the size and position.
Then you can download it as below: