Just in case anyone who still runs into the issue of using Topaz signature pad with Forms, the following are the steps to set up Topaz signature pad with Forms:

1. Make sure you have installed SigWeb(version 1.5) from here:
    https://www.topazsystems.com/software/sigweb_install.pdf
    and after installation, you can test whether the installation is successful by testing it at:
    www.sigplusweb.com/sigwebtablet_demo.htm

2. Add custom html field to the form

    a. Get SigWebTablet.js from http://www.sigplusweb.com/SigWebTablet.js, you can just copy and paste from the page and save it into a file named as "SigWebTablet.js"
    b. Put SigWebTablet.js file into Forms/lib/
    (You can put the file anywhere in the project as long as it is the same as the src path in the script tag so that the file can be referred) 
    c. In form designer, under Layout tab, drag a Custom Html field to the canvas, and inside Custom Html field, under Basic tab,  click on Html tab,  and paste in the following line:
 

        <script src="/Forms/lib/SigWebTablet.js"></script>

3. Change forms.js
    a.    Locate the file, “forms.js”, which should be at “C:\Program Files\Laserfiche\Laserfiche Forms\Forms\js\form”
    b.    Create a backup copy of forms.js and name it as formsBackup.js just in case you break anything and want to revert back to the original version
    c.    Open forms.js and find the following line:

    if ((isMobileBrowser || $('#sigNav li.active').index() == 1) && Signature.sigPad.isEmpty())

    d.    Change the line to:

    if ((isMobileBrowser || $('#sigNav li.active').index() == 1) && Signature.sigPad.isEmpty() && $.initSigWeb == undefined)

4. Copy and paste the following js code into Form's CSS and Javascript editor in Form's layout designer

$.initSigWeb = function(){
  var ctx = $("#sigTabContent .signatureSettings").get(0).getContext('2d');
  
  $("#sigNav a:eq(0)").hide();
  $("#form-signature-dlg").on("shown.bs.modal", function(){
    $("#sigNav a:eq(1)").click();
    tmr = setInterval(SigWebRefresh, 50);
  	SetDisplayXSize(438);
  	SetDisplayYSize(150);
  	SetJustifyMode(0);
    SetTabletState(1, ctx, 100); 
    $("button.signSignatureBtn").removeAttr("disabled");
  });
  $("span.clearSignature").on("click", function(){
    SetLCDCaptureMode(1);
    KeyPadClearHotSpotList();
    ClearSigWindow(1);
    ClearTablet();
    $("button.signSignatureBtn").removeAttr("disabled");
    setTimeout(function(){SetLCDCaptureMode(2);}, 2000);
  });
  $("#form-signature-dlg").on("hidden.bs.modal", function(){
    SetLCDCaptureMode(1);
    KeyPadClearHotSpotList();
    ClearSigWindow(1);
    ClearTablet();
    SetTabletState(0, ctx, 100);
  });
}
     
$(document).ready(function(){
  if (!window.isPrintMode){
    $.initSigWeb();
  }
});

After you are done with all of the above 4 steps, you can try to restart IIS, and also do a hard refresh on the browser to make sure every change you made will be successfully loaded.