downloading multiple documents

Greetings, I will be selling PDF documents. When people order the "entire series" they receive multiple documents under one purchase. They receive an email with the multiple PDF download links (see first attached screenshot).

When clicking on the first download link in the email, the person is redirected to a login page on my website. When they enter their info. and click "login" a popup window at the bottom appears for them to download the document they clicked on in their email (see second attached screenshot).

PROBLEM: nothing lets the person know that, after logging in and downloading the first PDF, they need to go back to their email for the rest of their download links. They're just left sitting on the login page.

What's the best way to let people know, once they've logged in and downloaded their first PDF, to go back to their email for the rest of the links? A pop up window saying "please return to your email for rest of links" would be great, but redirection to another page with that message would work too...

ALSO: Please note in second screenshot, text "Please login first" appears twice. I found it only once under "configuration" > "languages" under the header ";order". If it's not entered twice there, can you please advise how else I can get rid of the duplication?

Thank you!!!!

Thanks so much for your reply. Then, maybe my settings are logging people out too fast...for example, if they get coffee, a phone call, or distracted and don't go to their email right away. For this situation, I'd like to keep people logged in for at least one or two hours. I looked and didn't see the option to set log in time duration. Is this possible?

Also, when people do get directed from the email link to the log in page, are you saying there's no possiblity for a just a pop up window upon login, with a message prompting them to return to their email for the rest of their downloads? This would be my highest preference.

Another option would be to clearly state at the beginning of their download email "if redirected to log in, once doing so, please return to this email for rest of downloads." Is this option only available in your commercial version?

Sorry for so many questions, just looking for the best way to handle this awkward situation.

Thank you again!

Edit to add: I'm sorry, but I've been look for the file you reference below - administrator/components/com_hikashop/classes/file.php - and cannot find it. I apologize for being so inexperienced but, can you tell a total newbie how to find this file? Can I get to it from the Hikashop dashboard? Many thanks.

Thanks so much for all your help!