Download PDF inside webview

Greetings to all, I tell you what is going on with me. Resolved that I am developing an apk to access a web site, everything went perfect, but within this site there are files to download in multiple formats, including pdf and it turns out that it does not work the download manager of mobile, I can access to other links without a problem, but to access the download link of any file that is inside the page itself does not work.
My question is, is There any function or workaround to perform the task that I am concerned with?

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It's not there

Try to use extension or use CustomWebView by @vknow360

I already have the extension but I don't know how to use it for that I download some file with the web viewer

Please read this for using the extension

Forgiveness does not explain to me well, I have the extension installed, but what is not is how to put in the blocks of the program for me to download a file inside webview