All of files in this folder are PDF files

Hi,

There are lots of PDF files in directory "D:\PDF_Folder".

A. All files in this folder are PDF files.
B. All of files in this folder are PDF files.

Are both A and B correct?
I had used "All files" and "All of files" and similar in some technical documents, now I need to find the exact difference between them.
Please help, thanks.

I consider B incorrect because 'the' is missing before 'files'.

The final "files" is a bit redundant. In real life, you would hear "are pdfs."

Why is the "the" required?

A. All of the books ...
B. All of the peoples ...
C. All of the "[any noun]"s ...

D. All of books ...
E. All of peoples ...
F. All of "[any noun]"s ...

Based on the answer, then, ABC is correct, DEF is incorrect, right? Is it applied to all situation?

Pretty much all common nouns require an article.

fenglish said:

Why is the "the" required?

Click to expand...

I think it is because you are referring to the specific files in the folder rather than unspecified ones.

SoothingDave said:

The final "files" is a bit redundant. In real life, you would hear "are pdfs."

Click to expand...

And you might see PDFs.