There is a way, but this is kind of tricky. First of all, you need to attach your PDFs to templates by reference. This will require to set PR_ATTACH_METHOD MAPI property to ATTACH_BY_REF_ONLY (value of 4) and set some additional properties like PR_ATTACH_PATHNAME / PR_ATTACH_LONG_PATHNAME pointing to PDF file and save the template.

Then, you will need to replace the resulting links with attachments themselves before sending each message (based on the template).

You can write VBA scripts (quite complex) for that or use third-party tools. As one of the developers, I can recommend free Replace Attachments with Links and Restore Attachments from Links utilities.

There is a way, but this is kind of tricky. First of all, you need to attach your PDFs to templates by reference. This will require to set PR_ATTACH_METHOD MAPI property to ATTACH_BY_REF_ONLY (value of 4) and set some additional properties like PR_ATTACH_PATHNAME / PR_ATTACH_LONG_PATHNAME pointing to PDF file and save the template.

Then, you will need to replace the resulting links with attachments themselves before sending each message (based on the template).

You can write VBA scripts (quite complex) for that or use third-party tools. As one of the developers, I can recommend free Replace Attachments with Links and Restore Attachments from Links utilities. There is a tutorial video available (it covers the commercial product, but it almost the same for free tools).