Alexandru Vornicescu

If you want to download external images in your posts automatically so the page will use local image files instead of external image files then this plugin can help you.
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/1dZZ5ucNlQY?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>
It will replace the URLs of all external images (if the image has a different host URL) in your posts.
The URLs will get replaced with a local image copy URLs.
The action will be made on the post/page preview, not in the admin Edit page or after post save.
All the images that will be saved to your uploads folder (wp-content\uploads), not to your Media Library page.
This plugin can make your work faster if you like to use external images from other sites and you would like not to lose times on uploading images into you library every time for every image.

Download External Images In Posts

IT WORKS

This is the worst concept I have ever seen. This plugin should be reported.

I don't know what is the main concept of the plugin is. If you enable this plugin and start working with it, it downloads 1 content 100th of times or every time when someone visits the post. Even it consumes storage because everytime someone visits, first the plugin downloads and files to internally and then serve.

Within the middle of the time, visitors need to wait for the download and serve the content.

Therefore, SORRY TO SAY BUT, THIS IS A FLOP PROJECT.

Worst concept - Advising to not to use

This plugin will download external images in your posts to your "wp-content/uploads" folder.

HuangYe WuDeng

This plugin generates PDF documents for visitors when they click the “Download as PDF” button below the post. Very useful if you plan to share your posts in PDF format. 
Note: You can replace the logo file logo.pngunder wp-content/plugins/down-as-pdf/images/ with your own. 
注意：请将wp-content/plugins/down-as-pdf/images/目录下面的logo.png文件替换成你自己网站的logo
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Hacklog Down As PDF

This plugin generates PDF documents for visitors when they click the "Download as PDF" button below the post.

Download External Images In Posts vs Hacklog Down As PDF