Unable to Edit PDF Given to me by a customer

I have Adobe Acrobat Reader DC (provided by my company). We have a PDF form that has some open text boxes/fields (i.e. customer name and address). We ask our customer to fill out this form and return it. Sometimes when we get the form back we are unable to make any edits to file. This does not happen often, maybe 1 out of 50 times. I have tried some of the suggestions I have seen in other forums with no results. I also noticed that the form we get back from the customer has red lines around the "text fields" where customers would enter their information, when we sent it it was black. I know these are not password protected. I have had other collegues try as well and they are not able to edit it. Does it matter what version of Adobe the customer is using? I would appreciate any help!