How Finder can find this file with long name?
I've tried creating a PDF file with that name on two machines and both immediately index the files and provide them in searches for any part of the name. I would be curious to the see the actual content of the file in case the content is somehow causing the indexer to fail, but then you say the indexes okay with shorter names, so it doesn't follow that the content is a problem.

Something you could do is try running mdls against the file. This should show you metadata that is recorded in the Spotlight index for the file. For example when I run it against the PDF I used for testing I get things like the following. You can see here the kMDItemDisplayName and kMDItemFSName are both pulled from the actual name of the file, as the document is just a random PDF about something else entirely that I simply renamed).

kMDItemAuthors                 = (
    se0896
)
kMDItemContentCreationDate     = 2014-12-11 11:38:01 +0000
kMDItemContentModificationDate = 2014-12-11 11:38:01 +0000
kMDItemContentType             = "com.adobe.pdf"
kMDItemContentTypeTree         = (
    "com.adobe.pdf",
    "public.data",
    "public.item",
    "public.composite-content",
    "public.content"
)
kMDItemCreator                 = "Microsoft® Word 2010"
kMDItemDateAdded               = 2015-03-22 22:30:07 +0000
kMDItemDisplayName             = "Hans-Jorg Oestern, Otmar Lorenz Trentz, Lorem Ipsum Lorem Vascular Injuries- Trauma Surgery I (European Manual of Medicine).pdf"
kMDItemEncodingApplications    = (
    "Microsoft\U00ae Word 2010"
)
kMDItemFSContentChangeDate     = 2014-12-11 11:38:01 +0000
kMDItemFSCreationDate          = 2014-12-11 11:38:01 +0000
kMDItemFSCreatorCode           = ""
kMDItemFSFinderFlags           = 0
kMDItemFSHasCustomIcon         = (null)
kMDItemFSInvisible             = 0
kMDItemFSIsExtensionHidden     = 0
kMDItemFSIsStationery          = (null)
kMDItemFSLabel                 = 0
kMDItemFSName                  = "Hans-Jorg Oestern, Otmar Lorenz Trentz, Lorem Ipsum Lorem Vascular Injuries- Trauma Surgery I (European Manual of Medicine).pdf"
kMDItemFSNodeCount             = (null)
kMDItemFSOwnerGroupID          = 20
kMDItemFSOwnerUserID           = 501
kMDItemFSSize                  = 132180
kMDItemFSTypeCode              = ""
kMDItemKind                    = "Portable Document Format (PDF)"
kMDItemLogicalSize             = 132180
kMDItemNumberOfPages           = 5
kMDItemPageHeight              = 841.92
kMDItemPageWidth               = 595.32
kMDItemPhysicalSize            = 135168
kMDItemSecurityMethod          = "None"
kMDItemTitle                   = "Job Title"
kMDItemVersion                 = "1.5"


Another thing you could try is running the manual import tool mdimport with the debug option against both versions of the file (i.e. the file with a long name and again with a short name) and check for differences in the data that is being extracted and imported into Spotlight's metadata stores. The following command (with the correct path to your file of course) should show you which importer is being used and which keys are being extracted. This might help diagnose the fault. This is also a way to force Spotlight to index (or reindex) a file, but I don't think I've ever found that to be necessary. NOTE: The easiest way to perform the following command is to type "mdimport -d 3 " and then drag and drop the file onto the Terminal window.

mdimport -d 3 /Users/USERNAME/Hans-Jorg\ Oestern\,\ Otmar\ Lorenz\ Trentz\,\ Lorem\ Ipsum\ Lorem\ Vascular\ Injuries-\ Trauma\ Surgery\ I\ \(European\ Manual\ of\ Medicine\).pdf"