A PDF form is a digital document that contains interactive fields, such as text boxes, checkboxes, and drop-down menus, allowing users to input information directly into the form. It maintains the layout and formatting of the original document, ensuring that it appears consistent across different devices and platforms. PDF forms are commonly used for applications, surveys, and data collection due to their ease of use and wide compatibility.

To sign a PDF form, you can type, draw, or insert an image of your handwritten signature or initials.

Click the Sign icon in the Fill & Sign toolbar, and then choose  to add your signature or just initials.

If you've already got a signature saved, just select it from the Sign options. Cclick on the PDF where you want to add your signature. If you are signing for the first time, proceed to the next step.

If you are signing for the first time, you will see the Signature or Initials panel depending on which you chose.

Below is an example of the Signature panel.

There are three options for how to add your signature.

Type: Select this to type your name into the field. You can choose from a selection of signature styles, just click Change Style to view a different style.

Draw: Draw your signature.

Image: Browse and  select an image of your signature.

Once you're done, click Apply, and click on the place you want the signature or initial to be on the PDF

The third option allows you to create a normal-appearing signature using a pen and paper if you have the means to scan or photograph it.  
For the best results, make a largish clear signature on a black piece of paper with a blue or black ink pen.

Then use a copier to scan it to yourself. If you don't have a copier, a cell phone picture is also adequate. It can be cropped and emailed to yourself. Make sure to save the picture, or change it into, a JPEG file.

To move the placed signature, click the field to highlight it and then use the arrow keys. To resize or delete the field, use the options in the field toolbar.