public void AddAttachmentPattern(
	string filenamePattern
)

Public Sub AddAttachmentPattern ( 
	filenamePattern As String
)

Parameters

filenamePattern

Type: SystemString
The attachment pattern.

The attachment pattern is a string (like !filename!) which denotes a placeholder to be replaced with the actual attachment filename during mail merge operation. When Replace(String, String) method is called with the value of pattern parameter equal to the filename pattern previously added with AddAttachmentPattern(String) method, the file denoted by the path specified in actualValue parameter of Replace(String, String) method will be automatically attached.

It's possible to add multiple attachments with the same pattern. For that, in the value which will replace the pattern you'll need to delimit multiple file paths with ";". Or, you can call AddAttachmentPattern(String) method multiple times to set several different attachment patterns.

Note
Pattern of the message template is case-sensitive! For instance, if the pattern is #filename# and the attachment patterns contain #FILENAME# and #filename#, then only #filename# will be replaced with the actual value.

Reference