Step 7: Once you are done with customizing the document, you simply need to save it as a PDF file. Step 6: If you would like to have a checkbox on the fillable PDF file, you can add it by visiting the Developer tab > Check Box Content Control. To customize the options available on the drop-down list or combo box, you will simply need to select Properties under the Developer tab. Step 5: To add a drop-down list or a combo box for any field that you would like to add multiple choices, you will simply need to select the Developer tab > click Drop-Down List Content Control or Combo Box Content Control. Repeat for all the other fillable fields. To add the text control, you will need to visit the Developer tab > select Rich Text Content Control or Plain Text Content Control. Step 4: For each item, you would like the users to enter some text, you will have to add some text control. Step 3: Type the text you would like to have on the fillable PDF file.