I keep receiving an error page when trying to download my return documents as a pdf.

Please click here to troubleshoot printing/downloading issues.

Here's some other ideas,

What file did you download?  Was it a .tax or .pdf or .txt file?  If it downloads as a .txt file, try changing the .txt to .pdf or use a different browser to download it.  It doesn't like Microsoft Edge so use something else like Chrome or Firefox.

How to get a copy after filing

https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-get-a-copy-of-a-return-i-filed-this-year-in-turbotax-online/00/25932

Same here

You can find help with printing issues here.