You can select up to 100 documents to download at a time.
If you register for your personal account you can change the general settings so that your search will display up to 50 results per page.
Select the box at the top of the search results to select all of the documents on that page.
After you check the box the folder next to it will show that you have selected 50 documents.
Scroll to the bottom of the results to move to page 2 of the results and repeat the steps to add the next 50 documents to your folder. Your download is limited to 100 documents at a time. Select the three dots next to the download icon to make any changes to your download preferences.
If you do not select specific documents from your search results then the download button will download up to 250 items from the results list, but will not include the full text of those documents.
If the group of documents you are trying to download includes any web news documents you will get an error message "Web News documents are not supported for delivery at this time." You'll need to clear the delivery tray and eliminate the web news documents from your results, then reselect the documents to deliver.