diff --git a/pdf/model/colorspace.go b/pdf/model/colorspace.go
index d43d2d94..e5e23cfb 100644
--- a/pdf/model/colorspace.go
+++ b/pdf/model/colorspace.go
@@ -1521,9 +1521,8 @@ func (cs *PdfColorspaceLab) ColorToRGB(color PdfColor) (PdfColor, error) {
 	gFunc := func(x float64) float64 {
 		if x >= 6.0/29 {
 			return x * x * x
-		} else {
-			return 108.0 / 841 * (x - 4/29)
 		}
+		return 108.0 / 841 * (x - 4/29)
 	}
 
 	lab, ok := color.(*PdfColorLab)
@@ -1566,9 +1565,8 @@ func (cs *PdfColorspaceLab) ImageToRGB(img Image) (Image, error) {
 	g := func(x float64) float64 {
 		if x >= 6.0/29 {
 			return x * x * x
-		} else {
-			return 108.0 / 841 * (x - 4/29)
 		}
+		return 108.0 / 841 * (x - 4/29)
 	}
 
 	rgbImage := img
@@ -2111,7 +2109,7 @@ func (cs *PdfColorspaceSpecialPattern) ColorToRGB(color PdfColor) (PdfColor, err
 	}
 
 	if cs.UnderlyingCS == nil {
-		return nil, errors.New("underlying CS not defined.")
+		return nil, errors.New("underlying CS not defined")
 	}
 
 	return cs.UnderlyingCS.ColorToRGB(patternColor.Color)
diff --git a/pdf/model/font.go b/pdf/model/font.go
index fc23a791..8016e9f8 100644
--- a/pdf/model/font.go
+++ b/pdf/model/font.go
@@ -270,9 +270,9 @@ func newPdfFontFromPdfObject(fontObj core.PdfObject, allowType0 bool) (*PdfFont,
 				return nil, err
 			}
 			return &PdfFont{context: simplefont}, err
-		} else {
-			return nil, err
 		}
+
+		return nil, err
 	}
 
 	font := &PdfFont{}
diff --git a/pdf/model/fontfile.go b/pdf/model/fontfile.go
index 2ceeaac0..280e6aeb 100644
--- a/pdf/model/fontfile.go
+++ b/pdf/model/fontfile.go
@@ -105,7 +105,7 @@ func newFontFileFromPdfObject(obj core.PdfObject) (*fontFile, error) {
 // Based on pdfbox
 func (fontfile *fontFile) loadFromSegments(segment1, segment2 []byte) error {
 	common.Log.Trace("loadFromSegments: %d %d", len(segment1), len(segment2))
-	err := fontfile.parseAsciiPart(segment1)
+	err := fontfile.parseASCIIPart(segment1)
 	if err != nil {
 		return err
 	}
@@ -117,8 +117,8 @@ func (fontfile *fontFile) loadFromSegments(segment1, segment2 []byte) error {
 	return nil
 }
 
-// parseAsciiPart parses the ASCII part of the FontFile.
-func (fontfile *fontFile) parseAsciiPart(data []byte) error {
+// parseASCIIPart parses the ASCII part of the FontFile.
+func (fontfile *fontFile) parseASCIIPart(data []byte) error {
 
 	// Uncomment these lines to see the contents of the font file. For debugging.
 	// fmt.Println("~~~~~~~~~~~~~~~~~~~~~~~^^^~~~~~~~~~~~~~~~~~~~~~~~")
@@ -134,7 +134,7 @@ func (fontfile *fontFile) parseAsciiPart(data []byte) error {
 		return errors.New("invalid start of ASCII segment")
 	}
 
-	keySection, encodingSection, err := getAsciiSections(data)
+	keySection, encodingSection, err := getASCIISections(data)
 	if err != nil {
 		return err
 	}
@@ -170,14 +170,14 @@ var (
 	binaryStart   = "currentfile eexec"
 )
 
-// getAsciiSections returns two sections of `data`, the ASCII part of the FontFile
+// getASCIISections returns two sections of `data`, the ASCII part of the FontFile
 //   - the general key values in `keySection`
 //   - the encoding in `encodingSection`
-func getAsciiSections(data []byte) (keySection, encodingSection string, err error) {
-	common.Log.Trace("getAsciiSections: %d ", len(data))
+func getASCIISections(data []byte) (keySection, encodingSection string, err error) {
+	common.Log.Trace("getASCIISections: %d ", len(data))
 	loc := reDictBegin.FindIndex(data)
 	if loc == nil {
-		common.Log.Debug("ERROR: getAsciiSections. No dict.")
+		common.Log.Debug("ERROR: getASCIISections. No dict.")
 		return "", "", core.ErrTypeError
 	}
 	i0 := loc[1]
@@ -192,7 +192,7 @@ func getAsciiSections(data []byte) (keySection, encodingSection string, err erro
 	i2 := i1
 	i = strings.Index(string(data[i2:]), encodingEnd)
 	if i < 0 {
-		common.Log.Debug("ERROR: getAsciiSections. err=%v", err)
+		common.Log.Debug("ERROR: getASCIISections. err=%v", err)
 		return "", "", core.ErrTypeError
 	}
 	i3 := i2 + i
diff --git a/pdf/model/functions.go b/pdf/model/functions.go
index 231e231f..943d4dd5 100644
--- a/pdf/model/functions.go
+++ b/pdf/model/functions.go
@@ -507,10 +507,9 @@ func (f *PdfFunctionType2) ToPdfObject() core.PdfObject {
 	if f.container != nil {
 		f.container.PdfObject = dict
 		return f.container
-	} else {
-		return dict
 	}
 
+	return dict
 }
 
 func (f *PdfFunctionType2) Evaluate(x []float64) ([]float64, error) {
@@ -712,9 +711,9 @@ func (f *PdfFunctionType3) ToPdfObject() core.PdfObject {
 	if f.container != nil {
 		f.container.PdfObject = dict
 		return f.container
-	} else {
-		return dict
 	}
+
+	return dict
 }
 
 // PdfFunctionType4 is a Postscript calculator functions.
diff --git a/pdf/model/image.go b/pdf/model/image.go
index c78142bb..38fe02c4 100644
--- a/pdf/model/image.go
+++ b/pdf/model/image.go
@@ -10,11 +10,13 @@ import (
 	goimage "image"
 	gocolor "image/color"
 	"image/draw"
-	_ "image/gif"
-	_ "image/png"
 	"io"
 	"math"
 
+	// imported for initialization side effects.
+	_ "image/gif"
+	_ "image/png"
+
 	"github.com/unidoc/unidoc/common"
 	"github.com/unidoc/unidoc/pdf/core"
 	"github.com/unidoc/unidoc/pdf/internal/sampling"
diff --git a/pdf/model/internal/fonts/ttfparser.go b/pdf/model/internal/fonts/ttfparser.go
index 36da1534..28cf1eea 100644
--- a/pdf/model/internal/fonts/ttfparser.go
+++ b/pdf/model/internal/fonts/ttfparser.go
@@ -135,6 +135,7 @@ func (ttf *TtfType) MakeToUnicode() *cmap.CMap {
 	return cmap.NewToUnicodeCMap(codeToUnicode)
 }
 
+// NewEncoder returns a new TrueType font encoder.
 func (ttf *TtfType) NewEncoder() textencoding.TextEncoder {
 	return textencoding.NewTrueTypeFontEncoder(ttf.Chars)
 }
@@ -547,8 +548,8 @@ func (t *ttfParser) parseCmapFormat0() error {
 	data := []byte(dataStr)
 	common.Log.Trace("parseCmapFormat0: %s\ndataStr=%+q\ndata=[% 02x]", t.rec.String(), dataStr, data)
 
-	for code, glyphId := range data {
-		t.rec.Chars[rune(code)] = GID(glyphId)
+	for code, glyphID := range data {
+		t.rec.Chars[rune(code)] = GID(glyphID)
 	}
 	return nil
 }
@@ -562,8 +563,8 @@ func (t *ttfParser) parseCmapFormat6() error {
 		t.rec.String(), firstCode, entryCount)
 
 	for i := 0; i < entryCount; i++ {
-		glyphId := GID(t.ReadUShort())
-		t.rec.Chars[rune(i+firstCode)] = glyphId
+		glyphID := GID(t.ReadUShort())
+		t.rec.Chars[rune(i+firstCode)] = glyphID
 	}
 
 	return nil
@@ -589,16 +590,12 @@ func (t *ttfParser) parseCmapFormat12() error {
 		}
 
 		for j := uint32(0); j <= endCode-firstCode; j++ {
-			glyphId := startGlyph + j
-			// if glyphId >= numGlyphs {
-			// 	common.Log.Debug("ERROR: Format 12 cmap contains an invalid glyph index")
-			// 	break
-			// }
+			glyphID := startGlyph + j
 			if firstCode+j > 0x10FFFF {
 				common.Log.Debug("Format 12 cmap contains character beyond UCS-4")
 			}
 
-			t.rec.Chars[rune(i+firstCode)] = GID(glyphId)
+			t.rec.Chars[rune(i+firstCode)] = GID(glyphID)
 		}
 
 	}
diff --git a/pdf/model/page.go b/pdf/model/page.go
index 1fa06993..5d4e6173 100644
--- a/pdf/model/page.go
+++ b/pdf/model/page.go
@@ -422,7 +422,7 @@ func (p *PdfPage) getResources() (*PdfPageResources, error) {
 		if obj := dict.Get("Resources"); obj != nil {
 			prDict, ok := core.TraceToDirectObject(obj).(*core.PdfObjectDictionary)
 			if !ok {
-				return nil, errors.New("invalid resource dict!")
+				return nil, errors.New("invalid resource dict")
 			}
 			resources, err := NewPdfPageResourcesFromDict(prDict)
 
@@ -553,12 +553,11 @@ func (p *PdfPage) HasXObjectByName(name core.PdfObjectName) bool {
 	if !has {
 		return false
 	}
-
 	if obj := xresDict.Get(name); obj != nil {
 		return true
-	} else {
-		return false
 	}
+
+	return false
 }
 
 // GetXObjectByName gets XObject by name.
@@ -567,12 +566,11 @@ func (p *PdfPage) GetXObjectByName(name core.PdfObjectName) (core.PdfObject, boo
 	if !has {
 		return nil, false
 	}
-
 	if obj := xresDict.Get(name); obj != nil {
 		return obj, true
-	} else {
-		return nil, false
 	}
+
+	return nil, false
 }
 
 // HasFontByName checks if has font resource by name.
@@ -581,12 +579,11 @@ func (p *PdfPage) HasFontByName(name core.PdfObjectName) bool {
 	if !has {
 		return false
 	}
-
 	if obj := fontDict.Get(name); obj != nil {
 		return true
-	} else {
-		return false
 	}
+
+	return false
 }
 
 // HasExtGState checks if ExtGState name is available.
@@ -841,28 +838,25 @@ func (p *PdfPage) GetContentStreams() ([]string, error) {
 	if p.Contents == nil {
 		return nil, nil
 	}
-
 	contents := core.TraceToDirectObject(p.Contents)
-	if contArray, isArray := contents.(*core.PdfObjectArray); isArray {
-		// If an array of content streams, append it.
-		var cstreams []string
-		for _, cstreamObj := range contArray.Elements() {
-			cstreamStr, err := getContentStreamAsString(cstreamObj)
-			if err != nil {
-				return nil, err
-			}
-			cstreams = append(cstreams, cstreamStr)
-		}
-		return cstreams, nil
+
+	var cStreamObjs []core.PdfObject
+	if contArray, ok := contents.(*core.PdfObjectArray); ok {
+		cStreamObjs = contArray.Elements()
 	} else {
-		// Only 1 element in place. Wrap inside a new array and add the new one.
-		cstreamStr, err := getContentStreamAsString(contents)
+		cStreamObjs = []core.PdfObject{contents}
+	}
+
+	var cStreams []string
+	for _, cStreamObj := range cStreamObjs {
+		cStreamStr, err := getContentStreamAsString(cStreamObj)
 		if err != nil {
 			return nil, err
 		}
-		cstreams := []string{cstreamStr}
-		return cstreams, nil
+		cStreams = append(cStreams, cStreamStr)
 	}
+
+	return cStreams, nil
 }
 
 // GetAllContentStreams gets all the content streams for a page as one string.
diff --git a/pdf/model/pattern.go b/pdf/model/pattern.go
index ac678267..46d76b27 100644
--- a/pdf/model/pattern.go
+++ b/pdf/model/pattern.go
@@ -76,9 +76,9 @@ type PdfTilingPattern struct {
 func (p *PdfTilingPattern) IsColored() bool {
 	if p.PaintType != nil && *p.PaintType == 1 {
 		return true
-	} else {
-		return false
 	}
+
+	return false
 }
 
 // GetContentStream returns the pattern cell's content stream
diff --git a/pdf/model/reader.go b/pdf/model/reader.go
index 49a2d677..f6347e15 100755
--- a/pdf/model/reader.go
+++ b/pdf/model/reader.go
@@ -347,50 +347,32 @@ func (r *PdfReader) buildOutlineTree(obj core.PdfObject, parent *PdfOutlineTreeN
 		}
 
 		return &outlineItem.PdfOutlineTreeNode, &outlineItem.PdfOutlineTreeNode, nil
-	} else {
-		// Outline dictionary (structure element).
+	}
 
-		outline, err := newPdfOutlineFromIndirectObject(container)
+	// Outline dictionary (structure element).
+	outline, err := newPdfOutlineFromIndirectObject(container)
+	if err != nil {
+		return nil, nil, err
+	}
+	outline.Parent = parent
+
+	if firstObj := dict.Get("First"); firstObj != nil {
+		// Has children...
+		firstObj, err = r.traceToObject(firstObj)
 		if err != nil {
 			return nil, nil, err
 		}
-		outline.Parent = parent
-		//outline.Prev = parent
-
-		if firstObj := dict.Get("First"); firstObj != nil {
-			// Has children...
-			firstObj, err = r.traceToObject(firstObj)
+		if _, isNull := firstObj.(*core.PdfObjectNull); !isNull {
+			first, last, err := r.buildOutlineTree(firstObj, &outline.PdfOutlineTreeNode, nil)
 			if err != nil {
 				return nil, nil, err
 			}
-			if _, isNull := firstObj.(*core.PdfObjectNull); !isNull {
-				first, last, err := r.buildOutlineTree(firstObj, &outline.PdfOutlineTreeNode, nil)
-				if err != nil {
-					return nil, nil, err
-				}
-				outline.First = first
-				outline.Last = last
-			}
+			outline.First = first
+			outline.Last = last
 		}
-
-		/*
-			if nextObj, hasNext := (*dict)["Next"]; hasNext {
-				nextObj, err = r.traceToObject(nextObj)
-				if err != nil {
-					return nil, nil, err
-				}
-				if _, isNull := nextObj.(*PdfObjectNull); !isNull {
-					next, last, err := r.buildOutlineTree(nextObj, parent, &outline.PdfOutlineTreeNode)
-					if err != nil {
-						return nil, nil, err
-					}
-					outline.Next = next
-					return &outline.PdfOutlineTreeNode, last, nil
-				}
-			}*/
-
-		return &outline.PdfOutlineTreeNode, &outline.PdfOutlineTreeNode, nil
 	}
+
+	return &outline.PdfOutlineTreeNode, &outline.PdfOutlineTreeNode, nil
 }
 
 // GetOutlineTree returns the outline tree.
@@ -531,7 +513,7 @@ func (r *PdfReader) buildPageList(node *core.PdfIndirectObject, parent *core.Pdf
 	}
 	if *objType != "Pages" {
 		common.Log.Debug("ERROR: Table of content containing non Page/Pages object! (%s)", objType)
-		return errors.New("table of content containing non Page/Pages object!")
+		return errors.New("table of content containing non Page/Pages object")
 	}
 
 	// A Pages object.  Update the parent.
@@ -680,7 +662,7 @@ func (r *PdfReader) traverseObjectData(o core.PdfObject) error {
 
 	if _, isRef := o.(*core.PdfObjectReference); isRef {
 		common.Log.Debug("ERROR: Reader tracing a reference!")
-		return errors.New("reader tracing a reference!")
+		return errors.New("reader tracing a reference")
 	}
 
 	return nil
diff --git a/pdf/model/resources.go b/pdf/model/resources.go
index f079c581..2e51cdb4 100644
--- a/pdf/model/resources.go
+++ b/pdf/model/resources.go
@@ -119,12 +119,11 @@ func (r *PdfPageResources) GetExtGState(keyName core.PdfObjectName) (core.PdfObj
 		common.Log.Debug("ERROR: Invalid ExtGState entry - not a dict (got %T)", r.ExtGState)
 		return nil, false
 	}
-
 	if obj := dict.Get(keyName); obj != nil {
 		return obj, true
-	} else {
-		return nil, false
 	}
+
+	return nil, false
 }
 
 // HasExtGState checks whether a font is defined by the specified keyName.
@@ -145,7 +144,6 @@ func (r *PdfPageResources) GetShadingByName(keyName core.PdfObjectName) (*PdfSha
 		common.Log.Debug("ERROR: Invalid Shading entry - not a dict (got %T)", r.Shading)
 		return nil, false
 	}
-
 	if obj := shadingDict.Get(keyName); obj != nil {
 		shading, err := newPdfShadingFromPdfObject(obj)
 		if err != nil {
@@ -153,9 +151,9 @@ func (r *PdfPageResources) GetShadingByName(keyName core.PdfObjectName) (*PdfSha
 			return nil, false
 		}
 		return shading, true
-	} else {
-		return nil, false
 	}
+
+	return nil, false
 }
 
 // SetShadingByName sets a shading resource specified by keyName.
@@ -185,7 +183,6 @@ func (r *PdfPageResources) GetPatternByName(keyName core.PdfObjectName) (*PdfPat
 		common.Log.Debug("ERROR: Invalid Pattern entry - not a dict (got %T)", r.Pattern)
 		return nil, false
 	}
-
 	if obj := patternDict.Get(keyName); obj != nil {
 		pattern, err := newPdfPatternFromPdfObject(obj)
 		if err != nil {
@@ -194,9 +191,9 @@ func (r *PdfPageResources) GetPatternByName(keyName core.PdfObjectName) (*PdfPat
 		}
 
 		return pattern, true
-	} else {
-		return nil, false
 	}
+
+	return nil, false
 }
 
 // SetPatternByName sets a pattern resource specified by keyName.
@@ -226,12 +223,11 @@ func (r *PdfPageResources) GetFontByName(keyName core.PdfObjectName) (core.PdfOb
 		common.Log.Debug("ERROR: Font not a dictionary! (got %T)", core.TraceToDirectObject(r.Font))
 		return nil, false
 	}
-
 	if obj := fontDict.Get(keyName); obj != nil {
 		return obj, true
-	} else {
-		return nil, false
 	}
+
+	return nil, false
 }
 
 // HasFontByName checks whether a font is defined by the specified keyName.
@@ -293,9 +289,9 @@ func (r *PdfPageResources) HasXObjectByName(keyName core.PdfObjectName) bool {
 	obj, _ := r.GetXObjectByName(keyName)
 	if obj != nil {
 		return true
-	} else {
-		return false
 	}
+
+	return false
 }
 
 // GenerateXObjectName generates an unused XObject name that can be used for
diff --git a/pdf/model/structures.go b/pdf/model/structures.go
index 47a057b1..c5a1996b 100644
--- a/pdf/model/structures.go
+++ b/pdf/model/structures.go
@@ -152,9 +152,9 @@ func NewPdfDate(dateStr string) (PdfDate, error) {
 }
 
 // ToPdfObject converts date to a PDF string object.
-func (date *PdfDate) ToPdfObject() core.PdfObject {
+func (d *PdfDate) ToPdfObject() core.PdfObject {
 	str := fmt.Sprintf("D:%.4d%.2d%.2d%.2d%.2d%.2d%c%.2d'%.2d'",
-		date.year, date.month, date.day, date.hour, date.minute, date.second,
-		date.utOffsetSign, date.utOffsetHours, date.utOffsetMins)
+		d.year, d.month, d.day, d.hour, d.minute, d.second,
+		d.utOffsetSign, d.utOffsetHours, d.utOffsetMins)
 	return core.MakeString(str)
 }
diff --git a/pdf/model/writer.go b/pdf/model/writer.go
index 9aabec81..562eca12 100644
--- a/pdf/model/writer.go
+++ b/pdf/model/writer.go
@@ -431,7 +431,7 @@ func (w *PdfWriter) AddPage(page *PdfPage) error {
 
 	}
 	if *otype != "Page" {
-		return errors.New("Type != Page (Required).")
+		return errors.New("field Type != Page (Required)")
 	}
 
 	// Copy inherited fields if missing.