Hello Radek,

According to the Pdf Specification: When defining ranges of this type, care must be taken to ensure that the value of the last byte in the string is less than or equal to 255 − (srcCode2 − srcCode1). This ensures that the last byte of the string is not incremented past 255; otherwise, the result of the mapping is undefined and an error occurs. - from the "ToUnicode CMaps" section

The CMap in this document: 

16 0 obj
<< /Length 348 >>
stream
/CIDInit /ProcSet findresource begin
12 dict begin
begincmap
/CIDSystemInfo
<<
/Registry (Adobe)
/Ordering (UCS)
/Supplement 0
>> def
/CMapName /Adobe-Identity-UCS2 def
/CMapType 2 def
1 begincodespacerange
<0000> <ffff>
endcodespacerange
1 beginbfrange
<0000> <ffff> <0000>
endbfrange
endcmap
CMapName currentdict /CMap defineresource pop
end
end
endstream
endobj

And when you check the range "<0000> <ffff>", where srcCode2=65535 ("ffff") and srcCode1=0 ("0000"), so according to the stated above this makes this range invalid. So, the purpose of this feature request is to handle such invalid cases.

Regards,
Martin
Progress Telerik