Bridge CC 2017 Low image quality in Output PDF

[MarioPompei]

I have some A5 pdfs with text and bar codes.
In Bridge cc2017 i create a new Output PDF with 2 document in each A4 page (1 column, 2 raws), so I can print on a A4 laser printer avoiding paper waste.
I set the quality cursor to MAX and resolution to 300, but in the resulting PDF the quality is very low (the bar codes aren't readable). The original A5 documents are perfect. How can I solve the issue?
Thanks

[Lumigraphics]

Why not just print 2-up? You are going to lose quality by your method, you could try Acrobat Pro but I suspect it won't help.

[MarioPompei]

thanks Lumigraphcs.

How can I open a lot of original A5 PDFs and print them on a A4 printer?

[Lumigraphics]

What operating system are you on?