There is no standard method for showing the checkbox in PDF.
Showing a checkbox image in the print or using the following code snippet based on the check box field value.
<#if record.checkbox == true> [<span style=”color:green; font-size:12px;”> ✓ </span>] <!– Checkmark symbol –> <#else> [<span style=”color:red; font-size:12px;”> ✗ </span>] <!– Cross symbol –> </#if>