Dear Collagues of sdl community,

My source file is a pdf format and the software edition is SDL Trados Studio 2017. 

This error showed when I try to Pre-translate the project with my TM.

And I've tried all the methods mentioned in others' questions in the community, but none of them works.

I also utilized TMX editor to delete all the tags in that ID, apparently it didn't solve that either.   

Plus, if i transform the PDF format into a WORD document, it works just fine.

Since the original format is PDF, I am considering to keep it unchanged.

So, could anyone of you give me some kindly advice?

Thanks beforehand!