This question touches on several issues--all worthy of discussion.
First, there may be a security issue if applicants fill in a form and email it. Unless the pdf form handler encrypts the completed application, highly sensitive personal information could be intercepted during transmission to the bank. If there's any question about security, you should probably instruct applicants NOT to submit the form via email.
Next, be careful not to underestimate the actual scope of this project. I'm no authority on Reg B's appraisal rules, but the appraisal notification appears to be a boilerplate notice--with no transaction-specific content. The simplest of all possible methods can be used to e-deliver it, and who cares if the whole world sees it. Maybe your lenders have more in mind--including the "notice of action taken" (in case the decision is adverse), the copy of the actual appraisal, Reg. Z/RESPA disclosures, flood, and anything else you will need to deliver "in writing" during the processing of the application. Once you get to sensitive transaction-specific disclosures, security becomes mandatory. If you don't currently have a secure and efficient way to e-deliver these additional disclosures, don't agree to anything more than e-delivery of the boilerplate notice.
ESIGN consent for boilerplate e-delivery is very easy. Before you ask the applicant's consent, you must give the pre-consent disclosures. They don't have to be "in writing", so they can appear anywhere you can prove the customer saw them. Using a chain of pages, as you suggest, is a reliable way to do this. With appropriate explanation on the page containing the ESIGN preconsent disclosures, you can tell the applicant that the required appraisal notification will be displayed on the next page. If s/he can read this page, then you have adequate hardware and software to receive the appraisal notice and blank fill-in form. S/he can print or save this page as desired, but you should state that you won't provide a paper copy upon request. At the end of the preconsent disclosures, you will want to invite the applicant to click a button or link acknowledging these disclosures, consenting to receive the appraisal notice electronically, and acknowledging that there will be a link to the application form on the following page.
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...gone fishing.