Adober IFilter can not see Content of PDF Files and therefore Windows Contentsearch doesn't work

Hi, 

I work in IT and a costumer of mine has following issue. 

on the SQL Server we save many .pdf Files which are named with numbers. (1.pdf/2.pdf etc.)

Now I have a Microsoft Ticket open since May (When the issue appeared) and we can't seem to find a solution. MS was able to find out that Adobe IFilter can not see any Content of the PDF Files and therefore won't write down any Information in the Windows Search Database which is used for the Windows Search. 

We tried many thing already: 

- Updating 

- Reinstalling Adobe Reader / IFilter 

- Installing IFilter through HTTP and FTP 

- Uninstalling most Porgramms which work with pdf Files 

- Deactivating Anti Virus / Firewall

- .pdf Files are not temporary files (Attribute 0x20)

- Ownership of folder and permissions are ok

- Created another folder in C: Drive -> same issue 

- Checked Indexing Settings and reindexed folder 

- Checked Folderpermission to be indexed 

- all DISM / SFC commands

- restarted Windows Search Service

Kind regards,

Robin