Consider archiving them as djvu (<a href="http:&#x2F;&#x2F;djvu.sourceforge.net&#x2F;" rel="nofollow">http:&#x2F;&#x2F;djvu.sourceforge.net&#x2F;</a>).  One bit per pixel djvu files at 150PPI will likely become 2-5KB pages instead.<p>Djvu also supports a text layer just like PDF.<p>Note that 150PPI is barely better than FAX, so your documents will likely look &#x27;faxed&#x27; if you ever have to output hardcopies for some reason.