Just tested this in a plain Alloy 9.2 site with Episerver.Forms 0.19.4.9000 and I get docx and pdf uploads into the form submissions.

You're sure you added the file extensions as comma-separated, with no periods (.) ?

"docx, pdf"

I'm guessing you've tried it with file sizes below the maximum set in your web.config (or in your forms setup) - otherwise you'd get an error when submitting.

Are you getting a submission receipt message at all - are any form data submitted when the form includes a file upload?

Do you have any additional confirmation steps like sending email or something?

Yes, no periods.

I get no errors att all, "submit successful" is the message I get when submitting so everything is as it should, except it's not working.

I haven't done the email part, I only get the submitted forms in the Form Submissions section for now.

But the files should be included in the form subsmissions if it will be sent by email right?

The images that I upload appears in Forms Submissions, but all other files doesn't appear at all, it shows blank.

Yes the uploaded files should appear as clickable links in the forms submissions. 

So when submitting, you get the data in, but the file column is blank?

Which version of Episerver and Forms are you on?

Yes, all blank.

Latest version of both.

EpiServer is 9.6.1 and Forms is 0.21.1.9000

Solved the problem!

I didnt have the Generic Media Type model in my project.

http://world.episerver.com/documentation/Items/Developers-Guide/Episerver-CMS/8/Content/Assets-and-media/Media-types-and-templates/