It's unclear if your issue is the text being blurry or the images. But let's assume your images have the right resolution and were not resized bigger, or didn't lose any quality in that way.
If the texts are blurry, you can cheat and convert your PSD layer file to PDF, and still keep the sharpness of a vector.
From the screenshot that is still visible, it looks like a question of text trapping in Photoshop. You can fix this in 2 ways:
First Option: Don't flatten the text layers in Photoshop before exporting!
Let Photoshop flatten the layers during the export by checking the "as a copy" box while you export in PDF.
This way you will keep the "vector" properties of your text depending on the Photoshop version you use. When you flatten the whole layout before exporting, it rasterizes everything together.
You can keep the same settings for compression as the ones you already mentioned.
The examples below are both screenshots from Acrobat PDF:
Second Option: Convert that Photoshop text to vector
Simply save your file in .psd with the layers, and open that file in Illustrator. Choose the "convert layers to objects" and your text layers from Photoshop will be transformed into vectors.
How to keep the text in vector in Photoshop without rasterizing it or flattening the layers when exporting to PDF?
Now export that PDF with the highest quality setting or no compression at all, and open it again the way you took your screenshots to see if the issue still happens.
If you're satisfied, you can follow these instruction to optimize your PDF to be a smaller file size but retain the same print quality:
"Adobe PDF file too big, what are my options?"
Other Option: Add some trapping in Photoshop
If you don't own a license of Illustrator or simply don't want to use it, or you're using an older version of Photoshop, you could try to add some pixels to your trapping on your text. This will hide the anti-aliasing you might see on the final result but it will not improve the quality of your file Some colors don't blend well together and this will at least hide a bit the effect of anti-aliasing between the colors. It doesn't do miracles and your text and whole layout will still be a raster image.
To do this, go on the menu "image" and select "trap". In this box, add 1 or 2 pixels of trapping. Usually 2 gives good results.
Don't forget to keep another version of your Photoshop with layers; trapping like this will require your to flatten your file and you also need to be in CMYK color mode!
This is slightly destructive, it's good for some situations but if you can, it's better to convert your PDF to vector or use the first option above.
About PDF size/dimension
Acrobat doesn't open by default at 100% or fit to page; it depends on your preferences or the setting in the PDF as well. But you seem to have understood this already.
One reason why your PDF could look like being a different size than the Photoshop is the resolution set in the Adobe Acrobat Preferences.
Depending on what you have there, the "real size" of your PDF will vary on the screen. It's also normal
For example, the example below are the exact same PDF at 500% in Acrobat. The example on the right is using 72ppi display resolution in Acrobat and the one on the left is using 101ppi. I'm not certain but I think by default it's possible your page display is set to the system setting.
If you want to see the exact same size in Acrobat and Photoshop, and
that your Photoshop file is a 300ppi, try to insert 300ppi in the
Acrobat resolution setting. The 2 documents should be shown at the