This issue is attributed to some corrupted PDF files.
To identify the root cause of this error:

1. Make sure that the latest patches are applied to the IMSS application.
2. Create a policy in the IMSS management console to specifically process emails with PDF attachments.
   1. Log in to the IMSS management console.
   2. Go to Policy > Policy List.
   3. Click Add, and then select Recipients.
   4. Enter the email address that you want to use to receive the corrupted PDF attachment.
   5. Click Save, and then click Next.
   6. Under the Attachment section, enable the Name or extension check box and click Name or extension.
   7. Enable the Attachment named option.
   8. Enter "*.pdf" on the text field.
   9. Click Save, and then click Next.
   10. Under the Intercept section, select the Quarantine to [Default Quarantine] option.
   11. Under Monitor, enable the Archive modified to [Default Archive] option.
   12. Click Next.
   13. Enter "Before and After - PDF" on Rule Name field.
   14. Type "3" on Order Number field.
   15. Click Finish.
3. Set the log level to debug.
   1. Log in to the IMSS management console.
   2. Go to Logs > Settings.
   3. Under the Log Files section, set the value of Application log detail lever to "Debug".
   4. Click Save.
4. Replicate the problem.
   1. Create a message and enter the email address you indicated in Step 2-D as the recipient.
   2. Attach the PDF file.
   3. Save the email as *.EML or *.MSG file(s) before sending.
   4. Send the message and wait for a few minutes before proceeding to the next step.
5. Collect the quarantined and archived message.
   1. Log in to the IMSS management console.
   2. Go to Quarantine and Archive > Query > Quarantine tab.
   3. Enter the email address on Recipient(s) and click Display Log.
   4. Locate the message and get the Internal ID.
   5. Go to <imss_folder>\queue\quarantine\<first letter of Internal ID>/<second letter of Internal ID>.
   6. Get a copy of <Internal ID>.AF and <Internal ID>.DF.
6. Back up the tb_policy table by executing the following command:

   osql -U sa -P <sa_password>
   1> CREATE DATABASE imss_bak
   2> SELECT * INTO imss_bak..tb_policy FROM imss..tb_polic117725y
   3> BACKUP DATABASE imss_bak TO DISK="C:\imss_bak.dat"
   4> GO

7. Collect and submit the following to Trend Micro Technical Support.
    

   Compress the files using WinZip and apply the password "trend".
   • <Internal ID>.AF and <Internal ID>.DF from the Quarantine folder
   • <Internal ID>.AF and <Internal ID>.DF from the Archive folder
   • <imss_folder>\log\log.imss.yyyymmdd.*
   • <imss_folder>\log\mailtrace.yyyymmdd.*
   • <imss_folder>\log\tsmtpd.yyyymmdd.*
   • Copy of the saved message from Step 4-C
   • Copy of C:\imss_bak.dat