Attaching a png file vs a pdf - Why is there a difference?

[Toby]

Good day everyone,

I am working within a blog and attaching both png and pdf formatted files.
An attached png file embeds within the blog, while a pdf or pptx file stays attached below the blog.
Is there a reason the different file types behave differently and can this be changed? I have attached my settings to this post as well as what the different files look like in a blog. Sorry I cannot just supply a url, but my community is private.

Thank you for your help and suggestions.
Best,

Toby

[Toby]

An update -

When I attach a png file to a blog it automatically embeds into the body of the blog rather than staying as an attachment. Is this normal behavior for png files?

Why? Can this be changed?
Thank you,
Toby