how do I save combined pdfs as a binder, not as a portfolio?

I can't find it either.....

Thanks for your replied abhissha it worked for me using Creative Cloud Adobe Acrobat Reader. It is so simple; but their is not online help. It will make sense to have an option in Save As, or in the Preferences but there is not.  Searching with in Adobe is not efficient; not results.  Adobe have a tutorial explanation but it overlooks to mention the "Click on the Gear icon at the top center" hence, the final file is a Portfolio.

The links / tutorials below do not even mention the Gear.

How to combine and merge files into one PDF:

1. Within Acrobat, click on the Tools menu and select Combine Files.
2. Click Combine Files, and then click Add Files to select the files you want to include in your PDF.
3. Click, drag, and drop to reorder the files and pages. Double-click on a file to expand and rearrange individual pages. Press the Delete key to remove unwanted content.
4. When finished arranging files, click Combine Files.
5. Click the Save button.

Merge PDFs, combine files into one PDF | Adobe Acrobat DC

Overview of PDF Portfolios

Saving PDFs in Adobe Acrobat DC and Reader DC

Combine files into single PDF | Adobe Acrobat DC tutorials