Add reference PDFs for comparison purposes. Document comparison of example documents.

1 files changed, 13 insertions, 0 deletions

diff --git a/doc.go b/doc.go
index 3dd09ef..1561090 100644
--- a/doc.go
+++ b/doc.go
@@ -120,6 +120,19 @@ Please note that these examples run in the context of a test. In order run an
 example as a standalone application, you'll need to examine fpdf_test.go for
 some helper routines, for example exampleFilename and summary.
 
+Example PDFs can be compared with reference copies in order to verify that they
+have been generated as expected. This comparison will be performed if a PDF
+with the same name as the example PDF is placed in the gofpdf/pdf/reference
+directory. The routine that summarizes an example will look for this file and,
+if found, will call the ComparePDFFiles() to check the example PDF for equality
+with its reference PDF. If differences exist between the two files they will be
+printed to standard output and the test will fail. If the reference file is
+missing, the comparison is considered to succeed. In order to successfully
+compare two PDFs, the placement of internal resources must be consistent and
+the internal creation timestamps must be the same. To do this, the methods
+SetCatalogSort() and SetCreationDate() need to be called for both files. This
+is done automatically for all examples.
+
 Nonstandard Fonts
 
 Nothing special is required to use the standard PDF fonts (courier, helvetica,