I hope the following is useful, it's certainly simple and seems to work fine on iOS devices in addition to others.
You can download PDF.js from this link, I used the prebuilt (stable version).
https://mozilla.github.io/pdf.js/getting_started/Extract the files and you will have 2 folders (build and web) and a license terms file. I renamed the web folder to viewer, edited viewer.html as follows:
one simple edit, change the script reference to the location of pdf.js as below
<script src="/build/pdf.js"></script>
Copy the folders and subfolders to you applications web folder, the renamed folders don't clash with any standard folder names.
Simply insert the following html into your own web page at the appropriate position, please note file=%2Fgendocs%2FE0A59F8B-38E8-4607-9C73-179C93030D63.pdf
in this code refers to a subfolder of web called gendocs and the filename is E0A59F8B-38E8-4607-9C73-179C93030D63.pdf, the %2F represent the path / characters in the viewer file parameter structure, obviously use your own folder structure and filenames.
<div>
<iframe id="pdf-js-viewer" src="/viewer/viewer.html?file=%2Fgendocs%2FE0A59F8B-38E8-4607-9C73-179C93030D63.pdf" title="webviewer" STYLE="width:100%; height:1000px; overflow:auto; attribute:scrolling="no"; border:none"></iframe>
</div>
I hope this is useful, I'm no html expert so please feel free to improve on it and share the improvements.
Gordon