It is possible, although it is a little complex. I would need more information to assist with saving your page though. What web browser are you using? To save a page, there general answer is you would need to print it to PDF and automate those steps just as a user would. If you provide the browser, I could probably create an example of how to save a page as PDF. I know Chrome has a built-in printer to save to PDF, but I think for IE, you'd need to install one.
As for uploading a document to Pega, it is probably best to get this from an LSA as they may have a better solution than the one I am semi-familiar with. The basic steps of creating the activity are shown in the document attached, but the overall steps are;
Create an activity
Create a service package to call that activity
Create a REST service to call the service package
You would then take that file in your case and pass it to whatever you have to convert it to a TIFF.