Error combining files from ATO

Hi support,

We have a client that uses Adobe Acrobat Online in Chrome to combine and protect pdfs. A few days ago they mentioned the error "Can't combine files" appeared when they try to combine any pdf downloaded from the government ATO site. They mentioned before this they were able to. 

Process user takes:

1. Logs into ATO government site.

2. Opens report that they want to use.

3. Clicks print and Prints to PDF.

4. Saves it on local computer as pdf. 

5. Tries dragging file into combine with any other pdf, error occurs.

Troubleshooting steps taken:

1. Tried clearing cache

2. Tried combining with other pdfs not from ATO and they worked fine

3. Tried signing in and out of Adobe Reader Online.

4. Tried using Microsoft Edge and Firefox, same error appears.

3. Tried sending the files to another persons computer within the same company to try and combine the ATO pdf's, same issue.

4. Another person within the company tried downloading from ATO site, same error appears when combining those files.

5. Tried combining it myself outside of the company with the ATO files sent to me, same error appears.

At this point I did see a prompt the first time trying to combine the ATO files, which prompted:

'The file is either password protected, encrypted or is a PDF form that could not be combined to generate the PDF file.' It isn't password protected, not sure how to check if its encrypted, and it is a report not a form.

Would anyone know what my next steps would be? Thank you.