Sign in to Acrobat Web at https://documentcloud.adobe.com with your Adobe ID and password, or with your social (Facebook or Google) account. 

In the top navigation bar, click Edit > Combine Files.

Do one of the following to select the files that you want to combine and then click Continue:

• Choose files from the Recents or Documents list.
  
• Add files from your computer or drag-and-drop the files onto the highlighted area.
  
• You can also drag-and-drop files to the Combine Files tool on the Edit page.
  

To add more files, click Add Files or the plus icon before/after the file's thumbnail, select the desired files from the Recent or Files list or your computer, and then click Continue.

(Optional) Hover over a file and click the arrow to expand it and change its order in which you want it to appear in the combined PDF.

To move a page, expand the file, drag the page number box of the corresponding page thumbnail or the page thumbnail itself to the new location.

Enter a name for the combined PDF file, and then click Combine.

The files are converted and combined into one PDF, and then it's ready for download. Click the Download icon to save the file on your computer or device.

A copy of the combined PDF file is also stored in your Adobe Document Cloud account. The Recent section at the bottom area of the Home page lists all the files you’ve combined recently. Alternatively, to see the list of all your files, click Documents in the top-menu bar.