Create an Array Which Holds Each Character of Input

None of those.  A string is already defined as a character array.  Just access each character with array syntax.

for ($i = 1; $i < strlen($str); $i++) {
$nextchar = $str[$i];
// do something with $nextchar
}

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https://www.php.net/manual/en/language.types.string.php#language.types.string.details

First off, thank you for your reply. I really like your example, as it counts how many characters the string contains which is something I did not take into consideration. I am just a little confused how I would be able to write each character in a different location, separate from the other. I am not sure if this is considered "good" php, as I am somewhat of a newbie to php and programming in general. However, I was able to achieve my goal, using something like this:

$dl="L123456789012";
$dlSplit =(str_split($dl,1));
$pdf->Text(34, 94, $dlSplit[0]);
$pdf->Text(45, 94, $dlSplit[1]);
$pdf->Text(56, 94, $dlSplit[2]);
Doing so, allowed me to write each character in a different spot than the other.

That looks fine.  When you run out of characters, $dlSplit[x] is going to cause an error for a non-existent index 'x'.

I really like your code example. As stated before, I am new to programming, so I apologize ahead of time for my naiveness. If I wanted to implement your code, would this work:
for ($i = 1; $i < strlen($str); $i++) {
$x = 34;
$y =94;
$nextchar = $str[$i];
// do something with $nextchar
$pdf->Text($x, $y, $nextchar);
$x = $x + 11;
   if(strlen($str)> 15){
      $x=34;
      $y= 100;
      $pdf->Text($x, $y, $nextchar);
      $x = $x + 11;
  }
}

Basically, I would need to move the text along the X-axis by 11. If the string length is greater than 15 (which would be more than the number of boxes on the first line), I would need to move the text down the Y-axis by 6 and then move the text along the X-axis by 11.

This section is going to reset the position every time.  

 if(strlen($str)> 15

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You may need to move that to before the loop.

But, if the strlen is greater than 15, I need the text to shift on the Y-axis by a certain amount and then continue writing the text. So, if I put it before the for loop, will the text get written?

Where it is, the character will be written to the same position every time because you are resetting the position on every pass thru the loop.  Have you tried any of this yet?  Either it works or you learn.