to collaborate on SharePoint list attachment in pdf format

[nehals]

Hello guys .........we have nintex workflow for pdf files in list as attachments ........Is there a way to collaborate on SharePoint list attachment in pdf format? I am trying to check out the pdf file but it does not let me check in. What am I missing here?

[eharris04]

@nehals Checkin-checkout works for document libraries where the document is the main content type. 

Try reverting or using the workflow on a document library and see if it allows you to edit and check out the PDFs.