It seems you are trying to get the text out of a pdf just to replace the font, then make a new pdf..right? So getting the text out properly is the problem; try the things below.
Once you have the text out, by far your best bet to get a new pdf is to put the text into Writer or Word, format it the way you want, including the font, and export the new pdf from the word processor app. Trying to go pdf-->html-->epub-->pdf is just too hard and fraught with problems. No pdf on the planet will have styling information to allow you to get the text out and put it back with the same appearance. They just aren't made that way.
Calibre uses pdftohtml, a Popper tool, in it's attempts to convert pdf files. It is not always successful. There is a pdftotext tool that will sometimes work when the html tool fails. You called it "pdf2html" so you may have some completely different tool. There is no shortage of similar tools. Try here:
https://github.com/elswork/poppler-utils
The bottom line is there can be anything, any kind of garbage, in a pdf file and some of them are just about impossible to get good text out of. Another thing you might try is using an OCR tool to give the pdf your own text layer in one go, and then converting. Again there are many tools.
The last gasp is to do your own OCR page by page from screen shots. Or pull out png images with pdftopng, then OCR. Lots of work.
PDFs are mostly evil things in the ebook world, especially old ones made with who-knows what tools.