That is certainly an interesting one! I can see why watermarking your ebooks would be a good thing to do in terms of piracy prevention. I checked out that app you mentioned called Lemonink, and from what I can see on the app page it should allow you to watermark your PDF ebook files. Did you have specific issues with using the app that maybe the app developers could assist with? You can actually reach out to them directly by clicking the Get Support button on the app page and they should be happy to help.
I am assuming that you would need to place the watermark on the ebooks at the time of purchase, and you cannot do this ahead of time on an external application or online service? I had a look for other alternative apps in the Shopify App Store however it appears the one you have already tried is the obvious choice for this. If contacting the app developers for assistance doesn't help, then you could consider hiring a Shopify Expert. That would allow you to connect with freelance developers and agencies to work on a custom solution for your watermark requirement.
Have you created a collection on your online store and experienced an issue with adding yo...By Ollie Aug 24, 2022
Connect your PayPal account to allow your customers to checkout using the PayPal gateway a...By Ollie Jul 28, 2022