Fix for when 'trailer' is indented (#513)

* Fix for when 'trailer' is indented

Closes #214

* Address CR comments - strip line after parsing

* Update CHANGELOG.md

Co-authored-by: Pieter Marsman <pietermarsman@gmail.com>

CHANGELOG.md

@@ -31,6 +31,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Fixed
 - Rename PDFTextExtractionNotAllowedError to PDFTextExtractionNotAllowed to revert breaking change ([#461](https://github.com/pdfminer/pdfminer.six/pull/461))
 - Always try to get CMap, not only for identity encodings ([#438](https://github.com/pdfminer/pdfminer.six/pull/438))
+- Recognizing 'trailer' keyword with spaces as prefix or suffix ([#513](https://github.com/pdfminer/pdfminer.six/pull/513))
 
 ## [20200720]
 

pdfminer/pdfdocument.py

@@ -93,16 +93,15 @@ class PDFXRef(PDFBaseXRef):
         while True:
             try:
                 (pos, line) = parser.nextline()
-                if not line.strip():
+                line = line.strip()
+                if not line:
                     continue
             except PSEOF:
                 raise PDFNoValidXRef('Unexpected EOF - file corrupted?')
-            if not line:
-                raise PDFNoValidXRef('Premature eof: %r' % parser)
             if line.startswith(b'trailer'):
                 parser.seek(pos)
                 break
-            f = line.strip().split(b' ')
+            f = line.split(b' ')
             if len(f) != 2:
                 error_msg = 'Trailer not found: {!r}: line={!r}'\
                     .format(parser, line)
@@ -118,7 +117,7 @@ class PDFXRef(PDFBaseXRef):
                     (_, line) = parser.nextline()
                 except PSEOF:
                     raise PDFNoValidXRef('Unexpected EOF - file corrupted?')
-                f = line.strip().split(b' ')
+                f = line.split(b' ')
                 if len(f) != 3:
                     error_msg = 'Invalid XRef format: {!r}, line={!r}'\
                         .format(parser, line)