The iPhone and iPad versions of ContractorTools allow you to capture customers' signatures directly into estimate documents, but this requires your customer to have physical contact with your iPhone or iPad. If you use ContractorTools on a Mac, or if you need to have the customer sign the document from a remote location, you may want to have the customer sign "electronically".
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The issue of electronic signature is complicated because of legal requirements to ensure security and establish legitimacy, so we probably will not be adding it to ContractorTools soon, if ever. In the meantime, there are a number of third party electronic signature services that you can use with the PDF documents generated by ContractorTools:

SmallPDF: smallpdf.com/sign-pdf (free!)
DocuSign: www.docusign.com
HelloSign: www.hellosign.com
SigningHub: www.signinghub.com
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