diff --git a/user-doc/Files.txt b/user-doc/Files.txt
index f360af5d28e4a86540994c23ef7ce69bd9e6d5ca..55415587e90516f33390d40da226a8b7417a674a 100644
--- a/user-doc/Files.txt
+++ b/user-doc/Files.txt
@@ -46,6 +46,10 @@ If you provide a file for each replica (e.g. plumed.0.dat, plumed.1.dat, etc) yo
 setup plumed differently on each replica. 
 On the other hand, using a single plumed.dat will make all the replicas read the same file.
 
+\warning This rule is true for almost all the files read by PLUMED. Current exceptions
+  are PDB files, where the replica suffix is not added, and trajectories read by \ref driver,
+  for which the replica suffix is always added.
+
 Notice that when PLUMED adds the replica suffix, it recognizes the file extension and add the suffix _before_ the
 extension. Before PLUMED 2.2, the only recognized suffix was ".gz". Since 2.2, any suffix with length
 less or equal to five letters is recognized.
@@ -61,4 +65,5 @@ PLUMED will write files named COLVAR.0.gz, COLVAR.1.gz, test.0.HILLS, test.1.HIL
 etc. This is useful since the preserved extension makes it easy
 to process the files later.
 
+
 */