What type of attachment?   Do a search for:   All Content contains: sendFile

If you have a "File" attachment, the base64-encoded content is stored in ".pyAttachStream" whereas for Rule-File-Binary (R-F-B) attachments, the base64-encoded content is found in ".pyFileSource".

For the latter, i.e., R-F-Bs, take a look at Rule-File-Binary downloadFile Activity

For the former, i.e., Data-WorkAttach-File instances, see the Work-.DisplayAttachFile Activity.

You may also want to look at the Default • Base64Decode Function but you need to be careful as the Function says it returns a String which is not compatible with binary data due to character encoding.

Use alternative Base64Util methods that return either a byte[] array or an InputStream.

In particular consider using the byte[] array version of tools.sendFile() if using the Base64Decode.decode() Function.

EX:      tools.sendFile( myByteArray, myFileName, false, null, true);

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com.pega.pegarules.pub.uti
Class Base64Util

java.lang.Object
  com.pega.pegarules.pub.util.Base64Util

static byte[]                decode(byte[] aInByteArray)
static java.io.InputStream   decode(java.io.InputStream is)
static byte[]                decodeToByteArray(java.lang.String s)