Tell the client that’s not possible. It is okay to say no to a client especially when you know there’s nobody else that’s going to do it for free.
You were asked to do a job that you assumed was final. Offer to package the InDesign file or suggest InCopy.
Anything else would be some serious hoop jumping and you’ll regret it every week.
I was afraid it wasn't really possible. They already have the packaged file, they just don't want to spend any money to purchase InDesign or pay anyone else to make changes (hah!)
I'll look into InCopy. I think I have it with my CC subscription, but does the client also need to purchase InCopy for it to work?
Yes they do, and they’ll still need InDesign if they need to print it.
The term "deck" can refer to a presentation. You can export to PDF then to Powerpoint if that's the end game. Depending on the design, the content should be editable.