Currently in 78, the only filter rule is has/hasn't attachments, and it has never been possible (without add-ons) to filter by type of attachment. The only other rule that could be used is Size, since messages with pdf attachments are usually much larger than ones without. But again, there's no way to distinguish attachment types.

Many thanks for the answer. All messages with attachments can also be filtered, how does that work? Can you give me an add-on that can filter these messages?

well you create a filter that says if the message has an attachment do the following.

Information on Filters here https://support.mozilla.org/en-US/kb/organize-your-messages-using-filters

See the attached picture for an example. Note that Attachment Status only appears if the filter acts 'after Junk Classification'.