Embedding in Blogger
First you will need to upload/add the PDF you want to embed to your Google Drive, if it isn't there already, and make sure the share settings are 'anyone with the link can view' or 'public'. Then open it up, click the 3 vertical dots and choose 'open in new window'.
Copy the Embed Code
Now click on the 3 vertical dots to access a menu with the Embed item... option:
Embed the PDF into Blogger
Edit the post, and switch to HTML view, paste in the embed code (just stick it at the bottom, or the top if you're confused). Now switch back to Compose view, and you will see the PDF, you can centre it just like you would an image.
Where do you paste the HTML code? Click the HTML button, you'll see the blog post represented as code (well, technically it's script), find the place you want it, make a little space and paste it in. This is called embedding, </> and it's really useful for loads of things, any web tool that provides embed code, this is how you use it.
This is also where you can fiddle about with the settings to tweak the size of the window in your blog post to your satisfaction, look in the iframe script for the part where it says height="480" or/and width=640" or you can set the "...width=100%" to make it fill the width of the post.
Here's an example of how this looks in Blogger.
What if I want to Embed a Google Doc/Slide?
You can do that the same way, after publishing the Doc/Slide you will see an option to copy embed code, unfortunately that code doesn't include the height and width controls, but you can add those in yourself. I've created an example here so you can see how it works. Make sure the share settings are public, or anyone with a link can view...
To be honest though, it generally easier to just convert the doc/slide show into a PDF and embed that instead...