Export PDF failed. Cannot embed font Songti

For me it's the same. My solution was not to use the typeface 'Black' . After deleting it everythings works, strangely enough.

Sorry, but there are potentially big problems with this advice.

If indeed the font in question has restrictions within the font file itself (typically the fsType field of the OS2 table within OpenType - CFF or TTF flavors - or TrueType fonts), you had better check the actual EULA (End User License Agreement) for the actual restrictions on use of the font. Many if not most fonts that prohibit embedding also have clauses in their EULAs that prohibit outlining and or rasterization as “workarounds” to the embedding restrictions. They may or may not provide licenses for such fonts without such restrictions, but be prepared to pay higher licensing fees and potentially royalties for per PDF or per view use of the fonts in question.

Note that I am absolutely not trying to justify such antics on the part of various font foundries. You should always check on a font's licensing terms, including embeddability and royalties on distribution of content using the font (either as embedded or otherwise). Personally, I consider any font that has onerous restrictions either against embedding in PDF (or EPS or ePub) or distribution and use of such documents (requiring royalties) as a useless font.