" I write those blogs in texteditor" ... " I don't have the files locally"
Look contradictory, unless you mean some text area in a Web page. Are you using a blog or a CMS application? Often, those offer an export option.

" Export automatically the PDF form/template (made with Adobe Acrobat) that paste the text and images in the assigned fields."
I don't follow you there, perhaps that's my lack of PDF knowledge. What PDF forms (like those to input names and address?) have to do with getting a Web site?

" This way I can have a sleek archive from my blog items in the pdf format."
Not a very good archive format. It will be hard to get back HTML from there if you even need to restore a page, for some reason.
Beside, I don't understand either what you plan to do between XML and PDF. I know utilities to convert HTML to PDF, but from XML, it would need quite some processing (no pun intended) to format it nicely.

@phil.lho

So you want to get Web site as XML data, and export it to PDF with a given layout, different from the Web one.
I suggest to have a look at the iText Java library, it is one of the best to output PDF (it is used by Processing, actually).
But it won't be straightforward.