I'm an intern and my work consists in rewriting existing scripts running on a proprietary platform, using technologies (javascript, css, html and php) very different from the original ones (mostly vb6 on client's machine). I work in a regional detachment of the company and I'm the only one developing all our "regional" scripts.
The project manager understandably wants me to create a plan and give her general deadlines for each of the scripts: the problem is, there's insufficient (and in some cases zero) documentation on the original software. My senior stood up for me, but he's too being pressure to make functional requirements for those scripts (and all the people who worked on them don't work here anymore, so noone knows what they do in details).
These scripts are vital for the migration of the platform and the central company is pressuring every department to migrate, without giving us the resources to do so. Needless to say, we're all in deep shit, but how do I prevent myself from taking the blame if I screw up the time effort in the plan I need to make?