If you want to add fields to the document you've uploaded, you can find it under the Add tab. If you've uploaded a template from your library, you can add more fields to it and it won't effect the original template you chose.
These fields can be used to merge data to certain parts of your document, be input fields for the sender or recipient to fill in, or signature fields. To place a field on your doc, simply choose who the field will be connected to, then click and drag the field you'd like to add. There are three actions you can take once it's on your page:
Click and drag the body of the field to place it where you would like it on the page
Click and drag the corners of the field to resize it
Click the field and then the gear to edit its properties, such as who is taking the action on the field, the label of the text field, or setting a default value for the field
Click and drag around multiple fields to edit them all at once
You can also add supplemental files or URLs to your document to help your recipients make a decision, such as a demo video or terms and agreements.