Neither groff nor mandoc define .DS, .DE, or \f5.
Should probably be reported upstream after updating the port.

Index: sim.1
--- sim.1.orig
+++ sim.1
@@ -161,12 +161,12 @@ columns (default is
 The
 .B \-p
 option results in lines of the form
-.DS
-.ft 5
+.sp
+.RS
 F consists for x % of G material
-.ft P
-.DE
-meaning that \f5x\fP % of \f5F\fP's text can also be found in \f5G\fP.
+.RE
+.sp
+meaning that \fIx\fP % of \fIF\fP's text can also be found in \fIG\fP.
 Note that this relation is not symmetric; it is in fact quite possible for one
 file to consist for 100 % of text from another file, while the other file
 consists for only 1 % of text of the first file, if their lengths differ