I use Adobe Acrobat and MS Word. First original pdf has to be cleaned
up (removing non English languages) to get the best possible
conversion to .docx format. This makes it convenient to translate, but
sometimes the .docx file has to be repaired before translation (which
is true in this case) as the conversion never is perfect. Sometimes
better, other times worse.
After translation, .docx file most often has to be repaired/fixed
again, because of broken formatting, usually due to different size of
text but sometimes due to mistake by translator or CAT-tool.
Then conversion back to pdf, and afterwork to fix things that couldn’t
be fixed in .docx, optimisation of graphics and some magic to make
them look better.
That’s the process in a nutshell, and while it may sound simple a lot
of skill is needed to get it right, or a professional result rather
than a mediocre one.
As for the old client´s files, I did some work on those files to make
them look decent and readable, with various results depending on
available time as the client was in a hurry to get the translations.