RewriteEngine on
RewriteRule ^bill_signed_(.+)\.pdf$ admin/?controller=bills&action=print&hash=$1&signed=1 [NC,L]
RewriteRule ^bill_(.+)\.pdf$ admin/?controller=bills&action=print&hash=$1 [NC,L]
RewriteRule ^act_signed_(.+)\.pdf$ admin/?controller=acts&action=print&hash=$1&signed=1 [NC,L]
RewriteRule ^act_(.+)\.pdf$ admin/?controller=acts&action=print&hash=$1 [NC,L]